Method for signaling virtual boundary signaling with subpictures in coded video stream

ABSTRACT

A method, computer program, and computer system is provided for coding video data. Video data including one or more subpictures having one or more virtual boundaries is received. Information corresponding to the virtual boundaries is signaled in a picture parameter set, a picture header, or a slice header associated with the received video data. The video data is decoded based on the signaled information corresponding to the virtual boundaries.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority from U.S. Provisional PatentApplication No. 63/003,148, filed on Mar. 31, 2020, in the U.S. Patentand Trademark Office, which is incorporated herein by reference in itsentirety.

FIELD

This disclosure relates generally to field of data processing, and moreparticularly to video encoding and decoding.

BACKGROUND

Video coding and decoding using inter-picture prediction with motioncompensation has been known for decades. Uncompressed digital video canconsist of a series of pictures, each picture having a spatial dimensionof, for example, 1920×1080 luminance samples and associated chrominancesamples. The series of pictures can have a fixed or variable picturerate (informally also known as frame rate), of, for example 60 picturesper second or 60 Hz. Uncompressed video has significant bitraterequirements. For example, 1080p60 4:2:0 video at 8 bit per sample(1920×1080 luminance sample resolution at 60 Hz frame rate) requiresclose to 1.5 Gbit/s bandwidth. An hour of such video requires more than600 GByte of storage space.

One purpose of video coding and decoding can be the reduction ofredundancy in the input video signal, through compression. Compressioncan help reducing aforementioned bandwidth or storage spacerequirements, in some cases by two orders of magnitude or more. Bothlossless and lossy compression, as well as a combination thereof can beemployed. Lossless compression refers to techniques where an exact copyof the original signal can be reconstructed from the compressed originalsignal. When using lossy compression, the reconstructed signal may notbe identical to the original signal, but the distortion between originaland reconstructed signal is small enough to make the reconstructedsignal useful for the intended application. In the case of video, lossycompression is widely employed. The amount of distortion tolerateddepends on the application; for example, users of certain consumerstreaming applications may tolerate higher distortion than users oftelevision contribution applications. The compression ratio achievablecan reflect that: higher allowable/tolerable distortion can yield highercompression ratios.

A video encoder and decoder can utilize techniques from several broadcategories, including, for example, motion compensation, transform,quantization, and entropy coding, some of which will be introducedbelow.

Historically, video encoders and decoders tended to operate on a givenpicture size that was, in most cases, defined and stayed constant for acoded video sequence (CVS), Group of Pictures (GOP), or a similarmulti-picture timeframe. For example, in MPEG-2, system designs areknown to change the horizontal resolution (and, thereby, the picturesize) dependent on factors such as activity of the scene, but only at Ipictures, hence typically for a GOP. The resampling of referencepictures for use of different resolutions within a CVS is known, forexample, from ITU-T Rec. H.263 Annex P. However, here the picture sizedoes not change, only the reference pictures are being resampled,resulting potentially in only parts of the picture canvas being used (incase of downsampling), or only parts of the scene being captured (incase of upsampling). Further, H.263 Annex Q allows the resampling of anindividual macroblock by a factor of two (in each dimension), upward ordownward. Again, the picture size remains the same. The size of amacroblock is fixed in H.263, and therefore does not need to besignaled.

Changes of picture size in predicted pictures became more mainstream inmodern video coding. For example, VP9 allows reference pictureresampling and change of resolution for a whole picture. Similarly,certain proposals made towards VVC (including, for example, Hendry, et.al, “On adaptive resolution change (ARC) for VVC”, Joint Video Teamdocument JVET-M0135-v1, Jan. 9-19, 2019, incorporated herein in itsentirety) allow for resampling of whole reference pictures todifferent-higher or lower-resolutions. In that document, differentcandidate resolutions are suggested to be coded in the sequenceparameter set and referred to by per-picture syntax elements in thepicture parameter set.

SUMMARY

Embodiments relate to a method, system, and computer readable medium forcoding video data. According to one aspect, a method for coding videodata is provided. The method may include receiving video data includingone or more subpictures having one or more virtual boundaries.Information corresponding to the virtual boundaries is signaled in apicture parameter set, a picture header, or a slice header associatedwith the received video data. The video data is decoded based on thesignaled information corresponding to the virtual boundaries.

According to another aspect, a computer system for coding video data isprovided. The computer system may include one or more processors, one ormore computer-readable memories, one or more computer-readable tangiblestorage devices, and program instructions stored on at least one of theone or more storage devices for execution by at least one of the one ormore processors via at least one of the one or more memories, wherebythe computer system is capable of performing a method. The method mayinclude receiving video data including one or more subpictures havingone or more virtual boundaries. Information corresponding to the virtualboundaries is signaled in a picture parameter set, a picture header, ora slice header associated with the received video data. The video datais decoded based on the signaled information corresponding to thevirtual boundaries.

According to yet another aspect, a computer readable medium for codingvideo data is provided. The computer readable medium may include one ormore computer-readable storage devices and program instructions storedon at least one of the one or more tangible storage devices, the programinstructions executable by a processor. The program instructions areexecutable by a processor for performing a method that may accordinglyinclude receiving video data including one or more subpictures havingone or more virtual boundaries. Information corresponding to the virtualboundaries is signaled in a picture parameter set, a picture header, ora slice header associated with the received video data. The video datais decoded based on the signaled information corresponding to thevirtual boundaries.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other objects, features and advantages will become apparentfrom the following detailed description of illustrative embodiments,which is to be read in connection with the accompanying drawings. Thevarious features of the drawings are not to scale as the illustrationsare for clarity in facilitating the understanding of one skilled in theart in conjunction with the detailed description. In the drawings:

FIG. 1 is a schematic illustration of a simplified block diagram of acommunication system in accordance with an embodiment.

FIG. 2 is a schematic illustration of a simplified block diagram of acommunication system in accordance with an embodiment.

FIG. 3 is a schematic illustration of a simplified block diagram of adecoder in accordance with an embodiment.

FIG. 4 is a schematic illustration of a simplified block diagram of anencoder in accordance with an embodiment.

FIG. 5 is a schematic illustration of options for signaling ARCparameters in accordance with prior art or an embodiment, as indicated.

FIG. 6 is an example of a syntax table in accordance with an embodiment.

FIG. 7 is a schematic illustration of a computer system in accordancewith an embodiment.

FIG. 8 is an example of prediction structure for scalability withadaptive resolution change.

FIG. 9 is an example of a syntax table in accordance with an embodiment.

FIG. 10 is a schematic illustration of a simplified block diagram ofparsing and decoding poc cycle per access unit and access unit countvalue.

FIG. 11 is a schematic illustration of a video bitstream structurecomprising multi-layered sub-pictures.

FIG. 12 is a schematic illustration of a display of the selectedsub-picture with an enhanced resolution.

FIG. 13 is a block diagram of the decoding and display process for avideo bitstream comprising multi-layered sub-pictures.

FIG. 14 is a schematic illustration of 360 video display with anenhancement layer of a sub-picture.

FIG. 15 is an example of a layout information of sub-pictures and itscorresponding layer and picture prediction structure.

FIG. 16 is an example of a layout information of sub-pictures and itscorresponding layer and picture prediction structure, with spatialscalability modality of local region.

FIG. 17 is an example of a syntax table for sub-picture layoutinformation

FIG. 18 is an example of a syntax table of SEI message for sub-picturelayout information.

FIG. 19 is an example of a syntax table to indicate output layers andprofile/tier/level information for each output layer set.

FIG. 20 is an example of a syntax table to indicate output layer mode onfor each output layer set.

FIG. 21 is an example of a syntax table to indicate the presentsubpicture of each layer for each output layer set.

FIG. 22 is an example of a syntax table to indicate the subpictureidentifier.

FIG. 23 is an example of a syntax table to indicate the subpicturepartitioning information.

FIG. 24 is an example of a syntax table to virtual boundary informationin SPS.

FIG. 25 is an example of a syntax table to virtual boundary informationin picture header.

FIG. 26 is an example of a syntax table to virtual boundary informationin PPS.

DETAILED DESCRIPTION

Detailed embodiments of the claimed structures and methods are disclosedherein; however, it can be understood that the disclosed embodiments aremerely illustrative of the claimed structures and methods that may beembodied in various forms. Those structures and methods may, however, beembodied in many different forms and should not be construed as limitedto the exemplary embodiments set forth herein. Rather, these exemplaryembodiments are provided so that this disclosure will be thorough andcomplete and will fully convey the scope to those skilled in the art. Inthe description, details of well-known features and techniques may beomitted to avoid unnecessarily obscuring the presented embodiments.

As previously described, video encoders and decoders tended to operateon a given picture size that was, in most cases, defined and stayedconstant for a coded video sequence. However, a picture can bepartitioned into one or more subpictures. Each subpicture can be furtherpartitioned into one or more slices. Two or more independently codedsub-pictures may be merged into a coded picture, decoded by a decoder,and displayed as a single output picture. When a coded picture iscomposed of two or more coded subpictures, virtual boundaries may bepresent. It may be advantageous, therefore, for special handling of thevirtual boundaries.

Aspects are described herein with reference to flowchart illustrationsand/or block diagrams of methods, apparatus (systems), and computerreadable media according to the various embodiments. It will beunderstood that each block of the flowchart illustrations and/or blockdiagrams, and combinations of blocks in the flowchart illustrationsand/or block diagrams, can be implemented by computer readable programinstructions.

FIG. 1 illustrates a simplified block diagram of a communication system(100) according to an embodiment of the present disclosure. The system(100) may include at least two terminals (110-120) interconnected via anetwork (150). For unidirectional transmission of data, a first terminal(110) may code video data at a local location for transmission to theother terminal (120) via the network (150). The second terminal (120)may receive the coded video data of the other terminal from the network(150), decode the coded data and display the recovered video data.Unidirectional data transmission may be common in media servingapplications and the like.

FIG. 1 illustrates a second pair of terminals (130, 140) provided tosupport bidirectional transmission of coded video that may occur, forexample, during videoconferencing. For bidirectional transmission ofdata, each terminal (130, 140) may code video data captured at a locallocation for transmission to the other terminal via the network (150).Each terminal (130, 140) also may receive the coded video datatransmitted by the other terminal, may decode the coded data and maydisplay the recovered video data at a local display device.

In FIG. 1 , the terminals (110-140) may be illustrated as servers,personal computers and smart phones but the principles of the presentdisclosure may be not so limited. Embodiments of the present disclosurefind application with laptop computers, tablet computers, media playersand/or dedicated video conferencing equipment. The network (150)represents any number of networks that convey coded video data among theterminals (110-140), including for example wireline and/or wirelesscommunication networks. The communication network (150) may exchangedata in circuit-switched and/or packet-switched channels. Representativenetworks include telecommunications networks, local area networks, widearea networks and/or the Internet. For the purposes of the presentdiscussion, the architecture and topology of the network (150) may beimmaterial to the operation of the present disclosure unless explainedherein below.

FIG. 2 illustrates, as an example for an application for the disclosedsubject matter, the placement of a video encoder and decoder in astreaming environment. The disclosed subject matter can be equallyapplicable to other video enabled applications, including, for example,video conferencing, digital TV, storing of compressed video on digitalmedia including CD, DVD, memory stick and the like, and so on.

A streaming system may include a capture subsystem (213), that caninclude a video source (201), for example a digital camera, creating afor example uncompressed video sample stream (202). That sample stream(202), depicted as a bold line to emphasize a high data volume whencompared to encoded video bitstreams, can be processed by an encoder(203) coupled to the camera (201). The encoder (203) can includehardware, software, or a combination thereof to enable or implementaspects of the disclosed subject matter as described in more detailbelow. The encoded video bitstream (204), depicted as a thin line toemphasize the lower data volume when compared to the sample stream, canbe stored on a streaming server (205) for future use. One or morestreaming clients (206, 208) can access the streaming server (205) toretrieve copies (207, 209) of the encoded video bitstream (204). Aclient (206) can include a video decoder (210) which decodes theincoming copy of the encoded video bitstream (207) and creates anoutgoing video sample stream (211) that can be rendered on a display(212) or other rendering device (not depicted). In some streamingsystems, the video bitstreams (204, 207, 209) can be encoded accordingto certain video coding/compression standards. Examples of thosestandards include ITU-T Recommendation H.265. Under development is avideo coding standard informally known as Versatile Video Coding or VVC.The disclosed subject matter may be used in the context of VVC.

FIG. 3 may be a functional block diagram of a video decoder (210)according to an embodiment of the present invention.

A receiver (310) may receive one or more codec video sequences to bedecoded by the decoder (210); in the same or another embodiment, onecoded video sequence at a time, where the decoding of each coded videosequence is independent from other coded video sequences. The codedvideo sequence may be received from a channel (312), which may be ahardware/software link to a storage device which stores the encodedvideo data. The receiver (310) may receive the encoded video data withother data, for example, coded audio data and/or ancillary data streams,that may be forwarded to their respective using entities (not depicted).The receiver (310) may separate the coded video sequence from the otherdata. To combat network jitter, a buffer memory (315) may be coupled inbetween receiver (310) and entropy decoder/parser (320) (“parser”henceforth). When receiver (310) is receiving data from a store/forwarddevice of sufficient bandwidth and controllability, or from anisosychronous network, the buffer (315) may not be needed, or can besmall. For use on best effort packet networks such as the Internet, thebuffer (315) may be required, can be comparatively large and canadvantageously of adaptive size.

The video decoder (210) may include an parser (320) to reconstructsymbols (321) from the entropy coded video sequence. Categories of thosesymbols include information used to manage operation of the decoder(210), and potentially information to control a rendering device such asa display (212) that is not an integral part of the decoder but can becoupled to it, as was shown in FIG. 2 . The control information for therendering device(s) may be in the form of Supplementary EnhancementInformation (SEI messages) or Video Usability Information (VUI)parameter set fragments (not depicted). The parser (320) mayparse/entropy-decode the coded video sequence received. The coding ofthe coded video sequence can be in accordance with a video codingtechnology or standard, and can follow principles well known to a personskilled in the art, including variable length coding, Huffman coding,arithmetic coding with or without context sensitivity, and so forth. Theparser (320) may extract from the coded video sequence, a set ofsubgroup parameters for at least one of the subgroups of pixels in thevideo decoder, based upon at least one parameter corresponding to thegroup. Subgroups can include Groups of Pictures (GOPs), pictures, tiles,slices, macroblocks, Coding Units (CUs), blocks, Transform Units (TUs),Prediction Units (PUs) and so forth. The entropy decoder/parser may alsoextract from the coded video sequence information such as transformcoefficients, quantizer parameter values, motion vectors, and so forth.

The parser (320) may perform entropy decoding/parsing operation on thevideo sequence received from the buffer (315), so to create symbols(321).

Reconstruction of the symbols (321) can involve multiple different unitsdepending on the type of the coded video picture or parts thereof (suchas: inter and intra picture, inter and intra block), and other factors.Which units are involved, and how, can be controlled by the subgroupcontrol information that was parsed from the coded video sequence by theparser (320). The flow of such subgroup control information between theparser (320) and the multiple units below is not depicted for clarity.

Beyond the functional blocks already mentioned, decoder 210 can beconceptually subdivided into a number of functional units as describedbelow. In a practical implementation operating under commercialconstraints, many of these units interact closely with each other andcan, at least partly, be integrated into each other. However, for thepurpose of describing the disclosed subject matter, the conceptualsubdivision into the functional units below is appropriate.

A first unit is the scaler/inverse transform unit (351). Thescaler/inverse transform unit (351) receives quantized transformcoefficient as well as control information, including which transform touse, block size, quantization factor, quantization scaling matrices,etc. as symbol(s) (321) from the parser (320). It can output blockscomprising sample values, that can be input into aggregator (355).

In some cases, the output samples of the scaler/inverse transform (351)can pertain to an intra coded block; that is: a block that is not usingpredictive information from previously reconstructed pictures, but canuse predictive information from previously reconstructed parts of thecurrent picture. Such predictive information can be provided by an intrapicture prediction unit (352). In some cases, the intra pictureprediction unit (352) generates a block of the same size and shape ofthe block under reconstruction, using surrounding already reconstructedinformation fetched from the current (partly reconstructed) picture(356). The aggregator (355), in some cases, adds, on a per sample basis,the prediction information the intra prediction unit (352) has generatedto the output sample information as provided by the scaler/inversetransform unit (351).

In other cases, the output samples of the scaler/inverse transform unit(351) can pertain to an inter coded, and potentially motion compensatedblock. In such a case, a Motion Compensation Prediction unit (353) canaccess reference picture memory (357) to fetch samples used forprediction. After motion compensating the fetched samples in accordancewith the symbols (321) pertaining to the block, these samples can beadded by the aggregator (355) to the output of the scaler/inversetransform unit (in this case called the residual samples or residualsignal) so to generate output sample information. The addresses withinthe reference picture memory form where the motion compensation unitfetches prediction samples can be controlled by motion vectors,available to the motion compensation unit in the form of symbols (321)that can have, for example X, Y, and reference picture components.Motion compensation also can include interpolation of sample values asfetched from the reference picture memory when sub-sample exact motionvectors are in use, motion vector prediction mechanisms, and so forth.

The output samples of the aggregator (355) can be subject to variousloop filtering techniques in the loop filter unit (356). Videocompression technologies can include in-loop filter technologies thatare controlled by parameters included in the coded video bitstream andmade available to the loop filter unit (356) as symbols (321) from theparser (320), but can also be responsive to meta-information obtainedduring the decoding of previous (in decoding order) parts of the codedpicture or coded video sequence, as well as responsive to previouslyreconstructed and loop-filtered sample values.

The output of the loop filter unit (356) can be a sample stream that canbe output to the render device (212) as well as stored in the referencepicture memory (356) for use in future inter-picture prediction.

Certain coded pictures, once fully reconstructed, can be used asreference pictures for future prediction. Once a coded picture is fullyreconstructed and the coded picture has been identified as a referencepicture (by, for example, parser (320)), the current reference picture(356) can become part of the reference picture buffer (357), and a freshcurrent picture memory can be reallocated before commencing thereconstruction of the following coded picture.

The video decoder 320 may perform decoding operations according to apredetermined video compression technology that may be documented in astandard, such as ITU-T Rec. H.265. The coded video sequence may conformto a syntax specified by the video compression technology or standardbeing used, in the sense that it adheres to the syntax of the videocompression technology or standard, as specified in the videocompression technology document or standard and specifically in theprofiles document therein. Also necessary for compliance can be that thecomplexity of the coded video sequence is within bounds as defined bythe level of the video compression technology or standard. In somecases, levels restrict the maximum picture size, maximum frame rate,maximum reconstruction sample rate (measured in, for example megasamplesper second), maximum reference picture size, and so on. Limits set bylevels can, in some cases, be further restricted through HypotheticalReference Decoder (HRD) specifications and metadata for HRD buffermanagement signaled in the coded video sequence.

In an embodiment, the receiver (310) may receive additional (redundant)data with the encoded video. The additional data may be included as partof the coded video sequence(s). The additional data may be used by thevideo decoder (320) to properly decode the data and/or to moreaccurately reconstruct the original video data. Additional data can bein the form of, for example, temporal, spatial, or SNR enhancementlayers, redundant slices, redundant pictures, forward error correctioncodes, and so on.

FIG. 4 may be a functional block diagram of a video encoder (203)according to an embodiment of the present disclosure.

The encoder (203) may receive video samples from a video source (201)(that is not part of the encoder) that may capture video image(s) to becoded by the encoder (203).

The video source (201) may provide the source video sequence to be codedby the encoder (203) in the form of a digital video sample stream thatcan be of any suitable bit depth (for example: 8 bit, 10 bit, 12 bit, .. . ), any colorspace (for example, BT.601 Y CrCB, RGB, . . . ) and anysuitable sampling structure (for example Y CrCb 4:2:0, Y CrCb 4:4:4). Ina media serving system, the video source (201) may be a storage devicestoring previously prepared video. In a videoconferencing system, thevideo source (203) may be a camera that captures local image informationas a video sequence. Video data may be provided as a plurality ofindividual pictures that impart motion when viewed in sequence. Thepictures themselves may be organized as a spatial array of pixels,wherein each pixel can comprise one or more sample depending on thesampling structure, color space, etc. in use. A person skilled in theart can readily understand the relationship between pixels and samples.The description below focusses on samples.

According to an embodiment, the encoder (203) may code and compress thepictures of the source video sequence into a coded video sequence (443)in real time or under any other time constraints as required by theapplication. Enforcing appropriate coding speed is one function ofController (450). Controller controls other functional units asdescribed below and is functionally coupled to these units. The couplingis not depicted for clarity. Parameters set by controller can includerate control related parameters (picture skip, quantizer, lambda valueof rate-distortion optimization techniques, . . . ), picture size, groupof pictures (GOP) layout, maximum motion vector search range, and soforth. A person skilled in the art can readily identify other functionsof controller (450) as they may pertain to video encoder (203) optimizedfor a certain system design.

Some video encoders operate in what a person skilled in the are readilyrecognizes as a “coding loop”. As an oversimplified description, acoding loop can consist of the encoding part of an encoder (430)(“source coder” henceforth) (responsible for creating symbols based onan input picture to be coded, and a reference picture(s)), and a (local)decoder (433) embedded in the encoder (203) that reconstructs thesymbols to create the sample data a (remote) decoder also would create(as any compression between symbols and coded video bitstream islossless in the video compression technologies considered in thedisclosed subject matter). That reconstructed sample stream is input tothe reference picture memory (434). As the decoding of a symbol streamleads to bit-exact results independent of decoder location (local orremote), the reference picture buffer content is also bit exact betweenlocal encoder and remote encoder. In other words, the prediction part ofan encoder “sees” as reference picture samples exactly the same samplevalues as a decoder would “see” when using prediction during decoding.This fundamental principle of reference picture synchronicity (andresulting drift, if synchronicity cannot be maintained, for examplebecause of channel errors) is well known to a person skilled in the art.

The operation of the “local” decoder (433) can be the same as of a“remote” decoder (210), which has already been described in detail abovein conjunction with FIG. 3 . Briefly referring also to FIG. 3 , however,as symbols are available and encoding/decoding of symbols to a codedvideo sequence by entropy coder (445) and parser (320) can be lossless,the entropy decoding parts of decoder (210), including channel (312),receiver (310), buffer (315), and parser (320) may not be fullyimplemented in local decoder (433).

An observation that can be made at this point is that any decodertechnology except the parsing/entropy decoding that is present in adecoder also necessarily needs to be present, in substantially identicalfunctional form, in a corresponding encoder. For this reason, thedisclosed subject matter focusses on decoder operation. The descriptionof encoder technologies can be abbreviated as they are the inverse ofthe comprehensively described decoder technologies. Only in certainareas a more detail description is required and provided below.

As part of its operation, the source coder (430) may perform motioncompensated predictive coding, which codes an input frame predictivelywith reference to one or more previously-coded frames from the videosequence that were designated as “reference frames.” In this manner, thecoding engine (432) codes differences between pixel blocks of an inputframe and pixel blocks of reference frame(s) that may be selected asprediction reference(s) to the input frame.

The local video decoder (433) may decode coded video data of frames thatmay be designated as reference frames, based on symbols created by thesource coder (430). Operations of the coding engine (432) mayadvantageously be lossy processes. When the coded video data may bedecoded at a video decoder (not shown in FIG. 4 ), the reconstructedvideo sequence typically may be a replica of the source video sequencewith some errors. The local video decoder (433) replicates decodingprocesses that may be performed by the video decoder on reference framesand may cause reconstructed reference frames to be stored in thereference picture cache (434). In this manner, the encoder (203) maystore copies of reconstructed reference frames locally that have commoncontent as the reconstructed reference frames that will be obtained by afar-end video decoder (absent transmission errors).

The predictor (435) may perform prediction searches for the codingengine (432). That is, for a new frame to be coded, the predictor (435)may search the reference picture memory (434) for sample data (ascandidate reference pixel blocks) or certain metadata such as referencepicture motion vectors, block shapes, and so on, that may serve as anappropriate prediction reference for the new pictures. The predictor(435) may operate on a sample block-by-pixel block basis to findappropriate prediction references. In some cases, as determined bysearch results obtained by the predictor (435), an input picture mayhave prediction references drawn from multiple reference pictures storedin the reference picture memory (434).

The controller (450) may manage coding operations of the video coder(430), including, for example, setting of parameters and subgroupparameters used for encoding the video data.

Output of all aforementioned functional units may be subjected toentropy coding in the entropy coder (445). The entropy coder translatesthe symbols as generated by the various functional units into a codedvideo sequence, by loss-less compressing the symbols according totechnologies known to a person skilled in the art as, for exampleHuffman coding, variable length coding, arithmetic coding, and so forth.

The transmitter (440) may buffer the coded video sequence(s) as createdby the entropy coder (445) to prepare it for transmission via acommunication channel (460), which may be a hardware/software link to astorage device which would store the encoded video data. The transmitter(440) may merge coded video data from the video coder (430) with otherdata to be transmitted, for example, coded audio data and/or ancillarydata streams (sources not shown).

The controller (450) may manage operation of the encoder (203). Duringcoding, the controller (450) may assign to each coded picture a certaincoded picture type, which may affect the coding techniques that may beapplied to the respective picture. For example, pictures often may beassigned as one of the following frame types:

An Intra Picture (I picture) may be one that may be coded and decodedwithout using any other frame in the sequence as a source of prediction.Some video codecs allow for different types of Intra pictures,including, for example Independent Decoder Refresh Pictures. A personskilled in the art is aware of those variants of I pictures and theirrespective applications and features.

A Predictive picture (P picture) may be one that may be coded anddecoded using intra prediction or inter prediction using at most onemotion vector and reference index to predict the sample values of eachblock.

A Bi-directionally Predictive Picture (B Picture) may be one that may becoded and decoded using intra prediction or inter prediction using atmost two motion vectors and reference indices to predict the samplevalues of each block. Similarly, multiple-predictive pictures can usemore than two reference pictures and associated metadata for thereconstruction of a single block.

Source pictures commonly may be subdivided spatially into a plurality ofsample blocks (for example, blocks of 4×4, 8×8, 4×8, or 16×16 sampleseach) and coded on a block-by-block basis. Blocks may be codedpredictively with reference to other (already coded) blocks asdetermined by the coding assignment applied to the blocks' respectivepictures. For example, blocks of I pictures may be codednon-predictively or they may be coded predictively with reference toalready coded blocks of the same picture (spatial prediction or intraprediction). Pixel blocks of P pictures may be coded non-predictively,via spatial prediction or via temporal prediction with reference to onepreviously coded reference pictures. Blocks of B pictures may be codednon-predictively, via spatial prediction or via temporal prediction withreference to one or two previously coded reference pictures.

The video coder (203) may perform coding operations according to apredetermined video coding technology or standard, such as ITU-T Rec.H.265. In its operation, the video coder (203) may perform variouscompression operations, including predictive coding operations thatexploit temporal and spatial redundancies in the input video sequence.The coded video data, therefore, may conform to a syntax specified bythe video coding technology or standard being used.

In an embodiment, the transmitter (440) may transmit additional datawith the encoded video. The video coder (430) may include such data aspart of the coded video sequence. Additional data may comprisetemporal/spatial/SNR enhancement layers, other forms of redundant datasuch as redundant pictures and slices, Supplementary EnhancementInformation (SEI) messages, Visual Usability Information (VUI) parameterset fragments, and so on.

Before describing certain aspects of the disclosed subject matter inmore detail, a few terms need to be introduced that will be referred toin the remainder of this description.

Sub-Picture henceforth refers to an, in some cases, rectangulararrangement of samples, blocks, macroblocks, coding units, or similarentities that are semantically grouped, and that may be independentlycoded in changed resolution. One or more sub-pictures may for a picture.One or more coded sub-pictures may form a coded picture. One or moresub-pictures may be assembled into a picture, and one or more subpictures may be extracted from a picture. In certain environments, oneor more coded sub-pictures may be assembled in the compressed domainwithout transcoding to the sample level into a coded picture, and in thesame or certain other cases, one or more coded sub-pictures may beextracted from a coded picture in the compressed domain.

Adaptive Resolution Change (ARC) henceforth refers to mechanisms thatallow the change of resolution of a picture or sub-picture within acoded video sequence, by the means of, for example, reference pictureresampling. ARC parameters henceforth refer to the control informationrequired to perform adaptive resolution change, that may include, forexample, filter parameters, scaling factors, resolutions of outputand/or reference pictures, various control flags, and so forth.

Above description is focused on coding and decoding a single,semantically independent coded video picture. Before describing theimplication of coding/decoding of multiple sub pictures with independentARC parameters and its implied additional complexity, options forsignaling ARC parameters shall be described.

Referring to FIG. 5 , shown are several novel options for signaling ARCparameters. As noted with each of the options, they have certainadvantages and certain disadvantages from a coding efficiency,complexity, and architecture viewpoint. A video coding standard ortechnology may choose one or more of these options, or options knownfrom previous art, for signaling ARC parameters. The options may not bemutually exclusive, and conceivably may be interchanged based onapplication needs, standards technology involved, or encoder's choice.

Classes of ARC parameters may include:

-   -   up/downsample factors, separate or combined in X and Y dimension    -   up/downsample factors, with an addition of a temporal dimension,        indicating constant speed zoom in/out for a given number of        pictures    -   Either of the above two may involve the coding of one or more        presumably short syntax elements that may point into a table        containing the factor(s).    -   resolution, in X or Y dimension, in units of samples, blocks,        macroblocks, CUs, or any other suitable granularity, of the        input picture, output picture, reference picture, coded picture,        combined or separately. If there are more than one resolution        (such as, for example, one for input picture, one for reference        picture) then, in certain cases, one set of values may be        inferred to from another set of values. Such could be gated, for        example, by the use of flags. For a more detailed example, see        below.    -   “warping” coordinates akin those used in H.263 Annex P, again in        a suitable granularity as described above. H.263 Annex P defines        one efficient way to code such warping coordinates, but other,        potentially more efficient ways could conceivably also be        devised. For example, the variable length reversible,        “Huffman”-style coding of warping coordinates of Annex P could        be replaced by a suitable length binary coding, where the length        of the binary code word could, for example, be derived from a        maximum picture size, possibly multiplied by a certain factor        and offset by a certain value, so to allow for “warping” outside        of the maximum picture size's boundaries.    -   up or downsample filter parameters. In the easiest case, there        may be only a single filter for up and/or downsampling. However,        in certain cases, it can be advantageous to allow more        flexibility in filter design, and that may require to signaling        of filter parameters. Such parameters may be selected through an        index in a list of possible filter designs, the filter may be        fully specified (for example through a list of filter        coefficients, using suitable entropy coding techniques), the        filter may be implicitly selected through up/downsample ratios        according which in turn are signaled according to any of the        mechanisms mentioned above, and so forth.

Henceforth, the description assumes the coding of a finite set ofup/downsample factors (the same factor to be used in both X and Ydimension), indicated through a codeword. That codeword canadvantageously be variable length coded, for example using theExt-Golomb code common for certain syntax elements in video codingspecifications such as H.264 and H.265. One suitable mapping of valuesto up/downsample factors can, for example, be according to the followingtable:

Codeword Ext-Golomb Code Original/Target resolution 0 1 1/1 1 010 1/1.5(upscale by 50%) 2 011 1.5/1 (downscale by 50%) 3 00100 1/2 (upscale by100%) 4 00101 2/1 (downscale by 100%)

Many similar mappings could be devised according to the needs of anapplication and the capabilities of the up and downscale mechanismsavailable in a video compression technology or standard. The table couldbe extended to more values. Values may also be represented by entropycoding mechanisms other than Ext-Golomb codes, for example using binarycoding. That may have certain advantages when the resampling factorswere of interest outside the video processing engines (encoder anddecoder foremost) themselves, for example by MANEs. It should be notedthat, for the (presumably) most common case where no resolution changeis required, an Ext-Golomb code can be chosen that is short; in thetable above, only a single bit. That can have a coding efficiencyadvantage over using binary codes for the most common case.

The number of entries in the table, as well as their semantics may befully or partially configurable. For example, the basic outline of thetable may be conveyed in a “high” parameter set such as a sequence ordecoder parameter set. Alternatively or in addition, one or more suchtables may be defined in a video coding technology or standard, and maybe selected through for example a decoder or sequence parameter set.

Henceforth, we describe how an upsample/downsample factor (ARCinformation), coded as described above, may be included in a videocoding technology or standard syntax. Similar considerations may applyto one, or a few, codewords controlling up/downsample filters. See belowfor a discussion when comparatively large amounts of data are requiredfor a filter or other data structures.

H.263 Annex P includes the ARC information 502 in the form of fourwarping coordinates into the picture header 501, specifically in theH.263 PLUSPTYPE (503) header extension. This can be a sensible designchoice when a) there is a picture header available, and b) frequentchanges of the ARC information are expected. However, the overhead whenusing H.263-style signaling can be quite high, and scaling factors maynot pertain among picture boundaries as picture header can be oftransient nature.

JVCET-M135-v1, cited above, includes the ARC reference information (505)(an index) located in a picture parameter set (504), indexing a table(506) including target resolutions that in turn is located inside asequence parameter set (507). The placement of the possible resolutionin a table (506) in the sequence parameter set (507) can, according toverbal statements made by the authors, be justified by using the SPS asan interoperability negotiation point during capability exchange.Resolution can change, within the limits set by the values in the table(506) from picture to picture by referencing the appropriate pictureparameter set (504).

Still referring to FIG. 5 , the following additional options may existto convey ARC information in a video bitstream. Each of those optionshas certain advantages over existing art as described above. The optionsmay be simultaneously present in the same video coding technology orstandard.

In an embodiment, ARC information (509) such as a resampling (zoom)factor may be present in a slice header, GOB header, tile header, ortile group header (tile group header henceforth) (508). This can beadequate of the ARC information is small, such as a single variablelength ue(v) or fixed length codeword of a few bits, for example asshown above. Having the ARC information in a tile group header directlyhas the additional advantage of the ARC information may be applicable toa sub picture represented by, for example, that tile group, rather thanthe whole picture. See also below. In addition, even if the videocompression technology or standard envisions only whole picture adaptiveresolution changes (in contrast to, for example, tile group basedadaptive resolution changes), putting the ARC information into the tilegroup header vis a vis putting it into an H.263-style picture header hascertain advantages from an error resilience viewpoint.

In the same or another embodiment, the ARC information (512) itself maybe present in an appropriate parameter set (511) such as, for example, apicture parameter set, header parameter set, tile parameter set,adapation parameter set, and so forth (Adapation parameter setdepicted). The scope of that parameter set can advantageously be nolarger than a picture, for example a tile group. The use of the ARCinformation is implicit through the activation of the relevant parameterset. For example, when a video coding technology or standardcontemplates only picture-based ARC, then a picture parameter set orequivalent may be appropriate.

In the same or another embodiment, ARC reference information (513) maybe present in a Tile Group header (514) or a similar data structure.That reference information (513) can refer to a subset of ARCinformation (515) available in a parameter set (516) with a scope beyonda single picture, for example a sequence parameter set, or decoderparameter set.

The additional level of indirection implied activation of a PPS from atile group header, PPS, SPS, as used in JVET-M0135-v1 appears to beunnecessary, as picture parameter sets, just as sequence parameter sets,can (and have in certain standards such as RFC3984) be used forcapability negotiation or announcements. If, however, the ARCinformation should be applicable to a sub picture represented, forexample, by a tile groups also, a parameter set with an activation scopelimited to a tile group, such as the Adaptation Parameter set or aHeader Parameter Set may be the better choice. Also, if the ARCinformation is of more than negligible size—for example contains filtercontrol information such as numerous filter coefficients—then aparameter may be a better choice than using a header (508) directly froma coding efficiency viewpoint, as those settings may be reusable byfuture pictures or sub-pictures by referencing the same parameter set.

When using the sequence parameter set or another higher parameter setwith a scope spanning multiple pictures, certain considerations mayapply:

-   -   1. The parameter set to store the ARC information table (516)        can, in some cases, be the sequence parameter set, but in other        cases advantageously the decoder parameter set. The decoder        parameter set can have an activation scope of multiple CVSs,        namely the coded video stream, i.e. all coded video bits from        session start until session teardown. Such a scope may be more        appropriate because possible ARC factors may be a decoder        feature, possibly implemented in hardware, and hardware features        tend not to change with any CVS (which in at least some        entertainment systems is a Group of Pictures, one second or less        in length). That said, putting the table into the sequence        parameter set is expressly included in the placement options        described herein, in particular in conjunction with point 2        below.    -   2. The ARC reference information (513) may advantageously be        placed directly into the picture/slice tile/GOB/tile group        header (tile group header henceforth) (514) rather than into the        picture parameter set as in JVCET-M0135-v1, The reason is as        follows: when an encoder wants to change a single value in a        picture parameter set, such as for example the ARC reference        information, then it has to create a new PPS and reference that        new PPS. Assume that only the ARC reference information changes,        but other information such as, for example, the quantization        matrix information in the PPS stays. Such information can be of        substantial size, and would need to be retransmitted to make the        new PPS complete. As the ARC reference information may be a        single codeword, such as the index into the table (513) and that        would be the only value that changes, it would be cumbersome and        wasteful to retransmit all the, for example, quantization matrix        information. Insofar, can be considerably better from a coding        efficiency viewpoint to avoid the indirection through the PPS,        as proposed in JVET-M0135-v1. Similarly, putting the ARC        reference information into the PPS has the additional        disadvantage that the ARC information referenced by the ARC        reference information (513) necessarily needs to apply to the        whole picture and not to a sub-picture, as the scope of a        picture parameter set activation is a picture.

In the same or another embodiment, the signaling of ARC parameters canfollow a detailed example as outlined in FIG. 6 . FIG. 6 depicts syntaxdiagrams in a representation as used in video coding standards since atleast 1993. The notation of such syntax diagrams roughly follows C-styleprogramming. Lines in boldface indicate syntax elements present in thebitstream, lines without boldface often indicate control flow or thesetting of variables.

A tile group header (601) as an exemplary syntax structure of a headerapplicable to a (possibly rectangular) part of a picture canconditionally contain, a variable length, Exp-Golomb coded syntaxelement dec_pic_size_idx (602) (depicted in boldface). The presence ofthis syntax element in the tile group header can be gated on the use ofadaptive resolution (603)—here, the value of a flag not depicted inboldface, which means that flag is present in the bitstream at the pointwhere it occurs in the syntax diagram. Whether or not adaptiveresolution is in use for this picture or parts thereof can be signaledin any high level syntax structure inside or outside the bitstream. Inthe example shown, it is signaled in the sequence parameter set asoutlined below.

Still referring to FIG. 6 , shown is also an excerpt of a sequenceparameter set (610). The first syntax element shown isadaptive_pic_resolution_change_flag (611). When true, that flag canindicate the use of adaptive resolution which, in turn may requirecertain control information. In the example, such control information isconditionally present based on the value of the flag based on the if( )statement in the parameter set (612) and the tile group header (601).

When adaptive resolution is in use, in this example, coded is an outputresolution in units of samples (613). The numeral 613 refers to bothoutput_pic_width_in_luma_samples and output_pic_height_in_luma_samples,which together can define the resolution of the output picture.Elsewhere in a video coding technology or standard, certain restrictionsto either value can be defined. For example, a level definition maylimit the number of total output samples, which could be the product ofthe value of those two syntax elements. Also, certain video codingtechnologies or standards, or external technologies or standards suchas, for example, system standards, may limit the numbering range (forexample, one or both dimensions must be divisible by a power of 2number), or the aspect ratio (for example, the width and height must bein a relation such as 4:3 or 16:9). Such restrictions may be introducedto facilitate hardware implementations or for other reasons, and arewell known in the art.

In certain applications, it can be advisable that the encoder instructsthe decoder to use a certain reference picture size rather thanimplicitly assume that size to be the output picture size. In thisexample, the syntax element reference_pic_size_present_flag (614) gatesthe conditional presence of reference picture dimensions (615) (again,the numeral refers to both width and height).

Finally, shown is a table of possible decoding picture width andheights. Such a table can be expressed, for example, by a tableindication (num_dec_pic_size_in_luma_samples_minus1) (616). The “minus1”can refer to the interpretation of the value of that syntax element. Forexample, if the coded value is zero, one table entry is present. If thevalue is five, six table entries are present. For each “line” in thetable, decoded picture width and height are then included in the syntax(617).

The table entries presented (617) can be indexed using the syntaxelement dec_pic_size_idx (602) in the tile group header, therebyallowing different decoded sizes—in effect, zoom factors—per tile group.

Certain video coding technologies or standards, for example VP9, supportspatial scalability by implementing certain forms of reference pictureresampling (signaled quite differently from the disclosed subjectmatter) in conjunction with temporal scalability, so to enable spatialscalability. In particular, certain reference pictures may be upsampledusing ARC-style technologies to a higher resolution to form the base ofa spatial enhancement layer. Those upsampled pictures could be refined,using normal prediction mechanisms at the high resolution, so to adddetail.

The disclosed subject matter can be used in such an environment. Incertain cases, in the same or another embodiment, a value in the NALunit header, for example the Temporal ID field, can be used to indicatenot only the temporal but also the spatial layer. Doing so has certainadvantages for certain system designs; for example, existing SelectedForwarding Units (SFU) created and optimized for temporal layer selectedforwarding based on the NAL unit header Temporal ID value can be usedwithout modification, for scalable environments. In order to enablethat, there may be a requirement for a mapping between the coded picturesize and the temporal layer is indicated by the temporal ID field in theNAL unit header.

In some video coding technologies, an Access Unit (AU) can refer tocoded picture(s), slice(s), tile(s), NAL Unit(s), and so forth, thatwere captured and composed into a the respective picture/slice/tile/NALunit bitstream at a given instance in time. That instance in time can bethe composition time.

In HEVC, and certain other video coding technologies, a picture ordercount (POC) value can be used for indicating a selected referencepicture among multiple reference picture stored in a decoded picturebuffer (DPB). When an access unit (AU) comprises one or more pictures,slices, or tiles, each picture, slice, or tile belonging to the same AUmay carry the same POC value, from which it can be derived that theywere created from content of the same composition time. In other words,in a scenario where two pictures/slices/tiles carry the same given POCvalue, that can be indicative of the two picture/slice/tile belonging tothe same AU and having the same composition time. Conversely, twopictures/tiles/slices having different POC values can indicate thosepictures/slices/tiles belonging to different AUs and having differentcomposition times.

In an embodiment of the disclosed subject matter, aforementioned rigidrelationship can be relaxed in that an access unit can comprisepictures, slices, or tiles with different POC values. By allowingdifferent POC values within an AU, it becomes possible to use the POCvalue to identify potentially independently decodablepictures/slices/tiles with identical presentation time. That, in turn,can enable support of multiple scalable layers without a change ofreference picture selection signaling (e.g. reference picture setsignaling or reference picture list signaling), as described in moredetail below.

It is, however, still desirable to be able to identify the AU apicture/slice/tile belongs to, with respect to otherpicture/slices/tiles having different POC values, from the POC valuealone. This can be achieved, as described below.

In the same or other embodiments, an access unit count (AUC) may besignaled in a high-level syntax structure, such as NAL unit header,slice header, tile group header, SEI message, parameter set or AUdelimiter. The value of AUC may be used to identify which NAL units,pictures, slices, or tiles belong to a given AU. The value of AUC may becorresponding to a distinct composition time instance. The AUC value maybe equal to a multiple of the POC value. By diving the POC value by aninteger value, the AUC value may be calculated. In certain cases,division operations can place a certain burden on decoderimplementations. In such cases, small restrictions in the numberingspace of the AUC values may allow to substitute the division operationby shift operations. For example, the AUC value may be equal to a MostSignificant Bit (MSB) value of the POC value range.

In the same embodiment, a value of POC cycle per AU (poc_cycle_au) maybe signaled in a high-level syntax structure, such as NAL unit header,slice header, tile group header, SEI message, parameter set or AUdelimiter. The poc_cycle_au may indicate how many different andconsecutive POC values can be associated with the same AU. For example,if the value of poc_cycle_au is equal to 4, the pictures, slices ortiles with the POC value equal to 0-3, inclusive, are associated withthe AU with AUC value equal to 0, and the pictures, slices or tiles withPOC value equal to 4-7, inclusive, are associated with the AU with AUCvalue equal to 1. Hence, the value of AUC may be inferred by dividingthe POC value by the value of poc_cycle_au.

In the same or another embodiment, the value of poc_cycle_au may bederived from information, located for example in the video parameter set(VPS), that identifies the number of spatial or SNR layers in a codedvideo sequence. Such a possible relationship is briefly described below.While the derivation as described above may save a few bits in the VPSand hence may improves coding efficiency, it can be advantageous toexplicitly code poc_cycle_au in an appropriate high level syntaxstructure hierarchically below the video parameter set, so to be able tominimize poc_cycle_au for a given small part of a bitstream such as apicture. This optimization may save more bits than can be saved throughthe derivation process above because POC values (and/or values of syntaxelements indirectly referring to POC) may be coded in low level syntaxstructures.

The techniques for signaling adaptive resolution parameters describedabove, can be implemented as computer software using computer-readableinstructions and physically stored in one or more computer-readablemedia. For example, FIG. 7 shows a computer system 700 suitable forimplementing certain embodiments of the disclosed subject matter.

The computer software can be coded using any suitable machine code orcomputer language, that may be subject to assembly, compilation,linking, or like mechanisms to create code comprising instructions thatcan be executed directly, or through interpretation, micro-codeexecution, and the like, by computer central processing units (CPUs),Graphics Processing Units (GPUs), and the like.

The instructions can be executed on various types of computers orcomponents thereof, including, for example, personal computers, tabletcomputers, servers, smartphones, gaming devices, internet of thingsdevices, and the like.

The components shown in FIG. 7 for computer system 700 are exemplary innature and are not intended to suggest any limitation as to the scope ofuse or functionality of the computer software implementing embodimentsof the present disclosure. Neither should the configuration ofcomponents be interpreted as having any dependency or requirementrelating to any one or combination of components illustrated in theexemplary embodiment of a computer system 700.

Computer system 700 may include certain human interface input devices.Such a human interface input device may be responsive to input by one ormore human users through, for example, tactile input (such as:keystrokes, swipes, data glove movements), audio input (such as: voice,clapping), visual input (such as: gestures), olfactory input (notdepicted). The human interface devices can also be used to capturecertain media not necessarily directly related to conscious input by ahuman, such as audio (such as: speech, music, ambient sound), images(such as: scanned images, photographic images obtain from a still imagecamera), video (such as two-dimensional video, three-dimensional videoincluding stereoscopic video).

Input human interface devices may include one or more of (only one ofeach depicted): keyboard 701, mouse 702, trackpad 703, touch screen 710,data-glove 704, joystick 705, microphone 706, scanner 707, camera 708.

Computer system 700 may also include certain human interface outputdevices. Such human interface output devices may be stimulating thesenses of one or more human users through, for example, tactile output,sound, light, and smell/taste. Such human interface output devices mayinclude tactile output devices (for example tactile feedback by thetouch-screen 710, data-glove 704, or joystick 705, but there can also betactile feedback devices that do not serve as input devices), audiooutput devices (such as: speakers 709, headphones (not depicted)),visual output devices (such as screens 710 to include CRT screens, LCDscreens, plasma screens, OLED screens, each with or without touch-screeninput capability, each with or without tactile feedback capability-someof which may be capable to output two dimensional visual output or morethan three dimensional output through means such as stereographicoutput; virtual-reality glasses (not depicted), holographic displays andsmoke tanks (not depicted)), and printers (not depicted).

Computer system 700 can also include human accessible storage devicesand their associated media such as optical media including CD/DVD ROM/RW720 with CD/DVD or the like media 721, thumb-drive 722, removable harddrive or solid state drive 723, legacy magnetic media such as tape andfloppy disc (not depicted), specialized ROM/ASIC/PLD based devices suchas security dongles (not depicted), and the like.

Those skilled in the art should also understand that term “computerreadable media” as used in connection with the presently disclosedsubject matter does not encompass transmission media, carrier waves, orother transitory signals.

Computer system 700 can also include interface to one or morecommunication networks. Networks can for example be wireless, wireline,optical. Networks can further be local, wide-area, metropolitan,vehicular and industrial, real-time, delay-tolerant, and so on. Examplesof networks include local area networks such as Ethernet, wireless LANs,cellular networks to include GSM, 3G, 4G, 5G, LTE and the like, TVwireline or wireless wide area digital networks to include cable TV,satellite TV, and terrestrial broadcast TV, vehicular and industrial toinclude CANBus, and so forth. Certain networks commonly require externalnetwork interface adapters that attached to certain general purpose dataports or peripheral buses (749) (such as, for example USB ports of thecomputer system 700; others are commonly integrated into the core of thecomputer system 700 by attachment to a system bus as described below(for example Ethernet interface into a PC computer system or cellularnetwork interface into a smartphone computer system). Using any of thesenetworks, computer system 700 can communicate with other entities. Suchcommunication can be uni-directional, receive only (for example,broadcast TV), uni-directional send-only (for example CANbus to certainCANbus devices), or bi-directional, for example to other computersystems using local or wide area digital networks. Certain protocols andprotocol stacks can be used on each of those networks and networkinterfaces as described above.

Aforementioned human interface devices, human-accessible storagedevices, and network interfaces can be attached to a core 740 of thecomputer system 700.

The core 740 can include one or more Central Processing Units (CPU) 741,Graphics Processing Units (GPU) 742, specialized programmable processingunits in the form of Field Programmable Gate Areas (FPGA) 743, hardwareaccelerators for certain tasks 744, and so forth. These devices, alongwith Read-only memory (ROM) 745, Random-access memory 746, internal massstorage such as internal non-user accessible hard drives, SSDs, and thelike 747, may be connected through a system bus 748. In some computersystems, the system bus 748 can be accessible in the form of one or morephysical plugs to enable extensions by additional CPUs, GPU, and thelike. The peripheral devices can be attached either directly to thecore's system bus 748, or through a peripheral bus 749. Architecturesfor a peripheral bus include PCI, USB, and the like.

CPUs 741, GPUs 742, FPGAs 743, and accelerators 744 can execute certaininstructions that, in combination, can make up the aforementionedcomputer code. That computer code can be stored in ROM 745 or RAM 746.Transitional data can be also be stored in RAM 746, whereas permanentdata can be stored for example, in the internal mass storage 747. Faststorage and retrieve to any of the memory devices can be enabled throughthe use of cache memory, that can be closely associated with one or moreCPU 741, GPU 742, mass storage 747, ROM 745, RAM 746, and the like.

The computer readable media can have computer code thereon forperforming various computer-implemented operations. The media andcomputer code can be those specially designed and constructed for thepurposes of the present disclosure, or they can be of the kind wellknown and available to those having skill in the computer software arts.

As an example and not by way of limitation, the computer system havingarchitecture 700, and specifically the core 740 can providefunctionality as a result of processor(s) (including CPUs, GPUs, FPGA,accelerators, and the like) executing software embodied in one or moretangible, computer-readable media. Such computer-readable media can bemedia associated with user-accessible mass storage as introduced above,as well as certain storage of the core 740 that are of non-transitorynature, such as core-internal mass storage 747 or ROM 745. The softwareimplementing various embodiments of the present disclosure can be storedin such devices and executed by core 740. A computer-readable medium caninclude one or more memory devices or chips, according to particularneeds. The software can cause the core 740 and specifically theprocessors therein (including CPU, GPU, FPGA, and the like) to executeparticular processes or particular parts of particular processesdescribed herein, including defining data structures stored in RAM 746and modifying such data structures according to the processes defined bythe software. In addition or as an alternative, the computer system canprovide functionality as a result of logic hardwired or otherwiseembodied in a circuit (for example: accelerator 744), which can operatein place of or together with software to execute particular processes orparticular parts of particular processes described herein. Reference tosoftware can encompass logic, and vice versa, where appropriate.Reference to a computer-readable media can encompass a circuit (such asan integrated circuit (IC)) storing software for execution, a circuitembodying logic for execution, or both, where appropriate. The presentdisclosure encompasses any suitable combination of hardware andsoftware.

FIG. 8 shows an example of a video sequence structure with combinationof temporal_id, layer_id, POC and AUC values with adaptive resolutionchange. In this example, a picture, slice or tile in the first AU withAUC=0 may have temporal_id=0 and layer_id=0 or 1, while a picture, sliceor tile in the second AU with AUC=1 may have temporal_id=1 andlayer_id=0 or 1, respectively. The value of POC is increased by 1 perpicture regardless of the values of temporal_id and layer_id. In thisexample, the value of poc_cycle_au can be equal to 2. Preferably, thevalue of poc_cycle_au may be set equal to the number of (spatialscalability) layers. In this example, hence, the value of POC isincreased by 2, while the value of AUC is increased by 1.

In the above embodiments, all or sub-set of inter-picture or inter-layerprediction structure and reference picture indication may be supportedby using the existing reference picture set (RPS) signaling in HEVC orthe reference picture list (RPL) signaling. In RPS or RPL, the selectedreference picture is indicated by signaling the value of POC or thedelta value of POC between the current picture and the selectedreference picture. For the disclosed subject matter, the RPS and RPL canbe used to indicate the inter-picture or inter-layer predictionstructure without change of signaling, but with the followingrestrictions. If the value of temporal_id of a reference picture isgreater than the value of temporal_id current picture, the currentpicture may not use the reference picture for motion compensation orother predictions. If the value of layer_id of a reference picture isgreater than the value of layer_id current picture, the current picturemay not use the reference picture for motion compensation or otherpredictions.

In the same and other embodiments, the motion vector scaling based onPOC difference for temporal motion vector prediction may be disabledacross multiple pictures within an access unit. Hence, although eachpicture may have a different POC value within an access unit, the motionvector is not scaled and used for temporal motion vector predictionwithin an access unit. This is because a reference picture with adifferent POC in the same AU is considered a reference picture havingthe same time instance. Therefore, in the embodiment, the motion vectorscaling function may return 1, when the reference picture belongs to theAU associated with the current picture.

In the same and other embodiments, the motion vector scaling based onPOC difference for temporal motion vector prediction may be optionallydisabled across multiple pictures, when the spatial resolution of thereference picture is different from the spatial resolution of thecurrent picture. When the motion vector scaling is allowed, the motionvector is scaled based on both POC difference and the spatial resolutionratio between the current picture and the reference picture.

In the same or another embodiment, the motion vector may be scaled basedon AUC difference instead of POC difference, for temporal motion vectorprediction, especially when the poc_cycle_au has non-uniform value (whenvps_contant_poc_cycle_per_au==0). Otherwise (whenvps_contant_poc_cycle_per_au==1), the motion vector scaling based on AUCdifference may be identical to the motion vector scaling based on POCdifference.

In the same or another embodiment, when the motion vector is scaledbased on AUC difference, the reference motion vector in the same AU(with the same AUC value) with the current picture is not scaled basedon AUC difference and used for motion vector prediction without scalingor with scaling based on spatial resolution ratio between the currentpicture and the reference picture.

In the same and other embodiments, the AUC value is used for identifyingthe boundary of AU and used for hypothetical reference decoder (HRD)operation, which needs input and output timing with AU granularity. Inmost cases, the decoded picture with the highest layer in an AU may beoutputted for display. The AUC value and the layer_id value can be usedfor identifying the output picture.

In an embodiment, a picture may consist of one or more sub-pictures.Each sub-picture may cover a local region or the entire region of thepicture. The region supported by a sub-picture may or may not beoverlapped with the region supported by another sub-picture. The regioncomposed by one or more sub-pictures may or may not cover the entireregion of a picture. If a picture consists of a sub-picture, the regionsupported by the sub-picture is identical to the region supported by thepicture.

In the same embodiment, a sub-picture may be coded by a coding methodsimilar to the coding method used for the coded picture. A sub-picturemay be independently coded or may be coded dependent on anothersub-picture or a coded picture. A sub-picture may or may not have anyparsing dependency from another sub-picture or a coded picture.

In the same embodiment, a coded sub-picture may be contained in one ormore layers. A coded sub-picture in a layer may have a different spatialresolution. The original sub-picture may be spatially re-sampled(up-sampled or down-sampled), coded with different spatial resolutionparameters, and contained in a bitstream corresponding to a layer.

In the same or another embodiment, a sub-picture with (W, H), where Windicates the width of the sub-picture and H indicates the height of thesub-picture, respectively, may be coded and contained in the codedbitstream corresponding to layer 0, while the up-sampled (ordown-sampled) sub-picture from the sub-picture with the original spatialresolution, with (W*S_(w,k), H*S_(h,k)), may be coded and contained inthe coded bitstream corresponding to layer k, where S_(w,k), S_(h,k)indicate the resampling ratios, horizontally and vertically. If thevalues of S_(w,k), S_(h),k are greater than 1, the resampling is equalto the up-sampling. Whereas, if the values of S_(w,k), S_(h,k) aresmaller than 1, the resampling is equal to the down-sampling.

In the same or another embodiment, a coded sub-picture in a layer mayhave a different visual quality from that of the coded sub-picture inanother layer in the same sub-picture or different subpicture. Forexample, sub-picture i in a layer, n, is coded with the quantizationparameter, Q_(i,n), while a sub-picture j in a layer, m, is coded withthe quantization parameter, Q_(j,m).

In the same or another embodiment, a coded sub-picture in a layer may beindependently decodable, without any parsing or decoding dependency froma coded sub-picture in another layer of the same local region. Thesub-picture layer, which can be independently decodable withoutreferencing another sub-picture layer of the same local region, is theindependent sub-picture layer. A coded sub-picture in the independentsub-picture layer may or may not have a decoding or parsing dependencyfrom a previously coded sub-picture in the same sub-picture layer, butthe coded sub-picture may not have any dependency from a coded picturein another sub-picture layer.

In the same or another embodiment, a coded sub-picture in a layer may bedependently decodable, with any parsing or decoding dependency from acoded sub-picture in another layer of the same local region. Thesub-picture layer, which can be dependently decodable with referencinganother sub-picture layer of the same local region, is the dependentsub-picture layer. A coded sub-picture in the dependent sub-picture mayreference a coded sub-picture belonging to the same sub-picture, apreviously coded sub-picture in the same sub-picture layer, or bothreference sub-pictures.

In the same or another embodiment, a coded sub-picture consists of oneor more independent sub-picture layers and one or more dependentsub-picture layers. However, at least one independent sub-picture layermay be present for a coded sub-picture. The independent sub-picturelayer may have the value of the layer identifier (layer_id), which maybe present in NAL unit header or another high-level syntax structure,equal to 0. The sub-picture layer with the layer_id equal to 0 is thebase sub-picture layer.

In the same or another embodiment, a picture may consist of one or moreforeground sub-pictures and one background sub-picture. The regionsupported by a background sub-picture may be equal to the region of thepicture. The region supported by a foreground sub-picture may beoverlapped with the region supported by a background sub-picture. Thebackground sub-picture may be a base sub-picture layer, while theforeground sub-picture may be a non-base (enhancement) sub-picturelayer. One or more non-base sub-picture layer may reference the samebase layer for decoding. Each non-base sub-picture layer with layer_idequal to a may reference a non-base sub-picture layer with layer_idequal to b, where a is greater than b.

In the same or another embodiment, a picture may consist of one or moreforeground sub-pictures with or without a background sub-picture. Eachsub-picture may have its own base sub-picture layer and one or morenon-base (enhancement) layers. Each base sub-picture layer may bereferenced by one or more non-base sub-picture layers. Each non-basesub-picture layer with layer_id equal to a may reference a non-basesub-picture layer with layer_id equal to b, where a is greater than b.

In the same or another embodiment, a picture may consist of one or moreforeground sub-pictures with or without a background sub-picture. Eachcoded sub-picture in a (base or non-base) sub-picture layer may bereferenced by one or more non-base layer sub-pictures belonging to thesame sub-picture and one or more non-base layer sub-pictures, which arenot belonging to the same sub-picture.

In the same or another embodiment, a picture may consist of one or moreforeground sub-pictures with or without a background sub-picture. Asub-picture in a layer a may be further partitioned into multiplesub-pictures in the same layer. One or more coded sub-pictures in alayer b may reference the partitioned sub-picture in a layer a.

In the same or another embodiment, a coded video sequence (CVS) may be agroup of the coded pictures. The CVS may consist of one or more codedsub-picture sequences (CSPS), where the CSPS may be a group of codedsub-pictures covering the same local region of the picture. A CSPS mayhave the same or a different temporal resolution than that of the codedvideo sequence.

In the same or another embodiment, a CSPS may be coded and contained inone or more layers. A CSPS may consist of one or more CSPS layers.Decoding one or more CSPS layers corresponding to a CSPS may reconstructa sequence of sub-pictures corresponding to the same local region.

In the same or another embodiment, the number of CSPS layerscorresponding to a CSPS may be identical to or different from the numberof CSPS layers corresponding to another CSPS.

In the same or another embodiment, a CSPS layer may have a differenttemporal resolution (e.g. frame rate) from another CSPS layer. Theoriginal (uncompressed) sub-picture sequence may be temporallyre-sampled (up-sampled or down-sampled), coded with different temporalresolution parameters, and contained in a bitstream corresponding to alayer.

In the same or another embodiment, a sub-picture sequence with the framerate, F, may be coded and contained in the coded bitstream correspondingto layer 0, while the temporally up-sampled (or down-sampled)sub-picture sequence from the original sub-picture sequence, withF*S_(t,k), may be coded and contained in the coded bitstreamcorresponding to layer k, where S_(t,k) indicates the temporal samplingratio for layer k. If the value of S_(t,k) is greater than 1, thetemporal resampling process is equal to the frame rate up conversion.Whereas, if the value of S_(t,k) is smaller than 1, the temporalresampling process is equal to the frame rate down conversion.

In the same or another embodiment, when a sub-picture with a CSPS layera is reference by a sub-picture with a CSPS layer b for motioncompensation or any inter-layer prediction, if the spatial resolution ofthe CSPS layer a is different from the spatial resolution of the CSPSlayer b, decoded pixels in the CSPS layer a are resampled and used forreference. The resampling process may need an up-sampling filtering or adown-sampling filtering.

In the same or another embodiment, FIG. 9 shows an example of syntaxtables to signal the syntax element of vps_poc_cycle_au in VPS (or SPS),which indicates the poc_cycle_au used for all picture/slices in a codedvideo sequence, and the syntax element of slice_poc_cycle_au, whichindicates the poc_cycle_au of the current slice, in slice header. If thePOC value increases uniformly per AU, vps_contant_poc_cycle_per_au inVPS is set equal to 1 and vps_poc_cycle_au is signaled in VPS. In thiscase, slice_poc_cycle_au is not explicitly signaled, and the value ofAUC for each AU is calculated by dividing the value of POC byvps_poc_cycle_au. If the POC value does not increase uniformly per AU,vps_contant_poc_cycle_per_au in VPS is set equal to 0. In this case,vps_access_unit_cnt is not signaled, while slice_access_unit_cnt issignaled in slice header for each slice or picture. Each slice orpicture may have a different value of slice_access_unit_cnt. The valueof AUC for each AU is calculated by dividing the value of POC byslice_poc_cycle_au. FIG. 10 shows a block diagram illustrating therelevant workflow.

In the same or other embodiments, even though the value of POC of apicture, slice, or tile may be different, the picture, slice, or tilecorresponding to an AU with the same AUC value may be associated withthe same decoding or output time instance. Hence, without anyinter-parsing/decoding dependency across pictures, slices or tiles inthe same AU, all or subset of pictures, slices or tiles associated withthe same AU may be decoded in parallel, and may be outputted at the sametime instance.

In the same or other embodiments, even though the value of POC of apicture, slice, or tile may be different, the picture, slice, or tilecorresponding to an AU with the same AUC value may be associated withthe same composition/display time instance. When the composition time iscontained in a container format, even though pictures correspond todifferent AUs, if the pictures have the same composition time, thepictures can be displayed at the same time instance.

In the same or other embodiments, each picture, slice, or tile may havethe same temporal identifier (temporal_id) in the same AU. All or subsetof pictures, slices or tiles corresponding to a time instance may beassociated with the same temporal sub-layer. In the same or otherembodiments, each picture, slice, or tile may have the same or adifferent spatial layer id (layer_id) in the same AU. All or subset ofpictures, slices or tiles corresponding to a time instance may beassociated with the same or a different spatial layer.

FIG. 11 shows an example video stream including a background video CSPSwith layer_id equal to 0 and multiple foreground CSPS layers. While acoded sub-picture may consist of one or more CSPS layers, a backgroundregion, which does not belong to any foreground CSPS layer, may consistof a base layer. The base layer may contain a background region andforeground regions, while an enhancement CSPS layer contain a foregroundregion. An enhancement CSPS layer may have a better visual quality thanthe base layer, at the same region. The enhancement CSPS layer mayreference the reconstructed pixels and the motion vectors of the baselayer, corresponding to the same region.

In the same or another embodiment, the video bitstream corresponding toa base layer is contained in a track, while the CSPS layerscorresponding to each sub-picture are contained in a separated track, ina video file.

In the same or another embodiment, the video bitstream corresponding toa base layer is contained in a track, while CSPS layers with the samelayer_id are contained in a separated track. In this example, a trackcorresponding to a layer k includes CSPS layers corresponding to thelayer k, only.

In the same or another embodiment, each CSPS layer of each sub-pictureis stored in a separate track. Each trach may or may not have anyparsing or decoding dependency from one or more other tracks.

In the same or another embodiment, each track may contain bitstreamscorresponding to layer i to layer j of CSPS layers of all or a subset ofsub-pictures, where 0<i=<j=<k, k being the highest layer of CSPS.

In the same or another embodiment, a picture consists of one or moreassociated media data including depth map, alpha map, 3D geometry data,occupancy map, etc. Such associated timed media data can be divided toone or multiple data sub-stream each of which corresponding to onesub-picture.

In the same or another embodiment, FIG. 12 shows an example of videoconference based on the multi-layered sub-picture method. In a videostream, one base layer video bitstream corresponding to the backgroundpicture and one or more enhancement layer video bitstreams correspondingto foreground sub-pictures are contained. Each enhancement layer videbitstream is corresponding to a CSPS layer. In a display, the picturecorresponding to the base layer is displayed by default. It contains oneor more user's picture in a picture (PIP). When a specific user isselected by a client's control, the enhancement CSPS layer correspondingto the selected user is decoded and displayed with the enhanced qualityor spatial resolution. FIG. 13 shows the diagram for the operation.

In the same or another embodiment, a network middle box (such as router)may select a subset of layers to send to a user depending on itsbandwidth. The picture/subpicture organization may be used for bandwidthadaptation. For instance, if the user doesn't have the bandwidth, therouter strips of layers or selects some subpictures due to theirimportance or based on used setup and this can be done dynamically toadopt to bandwidth.

FIG. 14 shows a use case of 360 video. When a spherical 360 picture isprojected onto a planar picture, the projection 360 picture may bepartitioned into multiple sub-pictures as a base layer. An enhancementlayer of a specific sub-picture may be coded and transmitted to aclient. A decoder may be able to decode both the base layer includingall sub-pictures and an enhancement layer of a selected sub-picture.When the current viewport is identical to the selected sub-picture, thedisplayed picture may have a higher quality with the decoded sub-picturewith the enhancement layer. Otherwise, the decoded picture with the baselayer can be displayed, with a low quality.

In the same or another embodiment, any layout information for displaymay be present in a file, as supplementary information (such as SEImessage or metadata). One or more decoded sub-pictures may be relocatedand displayed depending on the signaled layout information. The layoutinformation may be signaled by a streaming server or a broadcaster, ormay be regenerated by a network entity or a cloud server, or may bedetermined by a user's customized setting.

In an embodiment, when an input picture is divided into one or more(rectangular) sub-region(s), each sub-region may be coded as anindependent layer. Each independent layer corresponding to a localregion may have a unique layer_id value. For each independent layer, thesub-picture size and location information may be signaled. For example,picture size (width, height), the offset information of the left-topcorner (x_offset, y_offset). FIG. 15 shows an example of the layout ofdivided sub-pictures, its sub-picture size and position information andits corresponding picture prediction structure. The layout informationincluding the sub-picture size(s) and the sub-picture position(s) may besignaled in a high-level syntax structure, such as parameter set(s),header of slice or tile group, or SEI message.

In the same embodiment, each sub-picture corresponding to an independentlayer may have its unique POC value within an AU. When a referencepicture among pictures stored in DPB is indicated by using syntaxelement(s) in RPS or RPL structure, the POC value(s) of each sub-picturecorresponding to a layer may be used.

In the same or another embodiment, in order to indicate the(inter-layer) prediction structure, the layer_id may not be used and thePOC (delta) value may be used.

In the same embodiment, a sub-picture with a POC vale equal to Ncorresponding to a layer (or a local region) may or may not be used as areference picture of a sub-picture with a POC value equal to N+K,corresponding to the same layer (or the same local region) for motioncompensated prediction. In most cases, the value of the number K may beequal to the maximum number of (independent) layers, which may beidentical to the number of sub-regions.

In the same or another embodiment, FIG. 16 shows the extended case ofFIG. 15 . When an input picture is divided into multiple (e.g. four)sub-regions, each local region may be coded with one or more layers. Inthe case, the number of independent layers may be equal to the number ofsub-regions, and one or more layers may correspond to a sub-region.Thus, each sub-region may be coded with one or more independent layer(s)and zero or more dependent layer(s).

In the same embodiment, in FIG. 16 , the input picture may be dividedinto four sub-regions. The right-top sub-region may be coded as twolayers, which are layer 1 and layer 4, while the right-bottom sub-regionmay be coded as two layers, which are layer 3 and layer 5. In this case,the layer 4 may reference the layer 1 for motion compensated prediction,while the layer 5 may reference the layer 3 for motion compensation.

In the same or another embodiment, in-loop filtering (such as deblockingfiltering, adaptive in-loop filtering, reshaper, bilateral filtering orany deep-learning based filtering) across layer boundary may be(optionally) disabled.

In the same or another embodiment, motion compensated prediction orintra-block copy across layer boundary may be (optionally) disabled.

In the same or another embodiment, boundary padding for motioncompensated prediction or in-loop filtering at the boundary ofsub-picture may be processed optionally. A flag indicating whether theboundary padding is processed or not may be signaled in a high-levelsyntax structure, such as parameter set(s) (VPS, SPS, PPS, or APS),slice or tile group header, or SEI message.

In the same or another embodiment, the layout information ofsub-region(s) (or sub-picture(s)) may be signaled in VPS or SPS. FIG. 17shows an example of the syntax elements in VPS and SPS. In this example,vps_sub_picture_dividing_flag is signalled in VPS. The flag may indicatewhether input picture(s) are divided into multiple sub-regions or not.When the value of vps_sub_picture_dividing_flag is equal to 0, the inputpicture(s) in the coded video sequence(s) corresponding to the currentVPS may not be divided into multiple sub-regions. In this case, theinput picture size may be equal to the coded picture size(pic_width_in_luma_samples, pic_height_in_luma_samples), which issignaled in SPS. When the value of vps_sub_picture_dividing_flag isequal to 1, the input picture(s) may be divided into multiplesub-regions. In this case, the syntax elementsvps_full_pic_width_in_luma_samples andvps_full_pic_height_in_luma_samples are signaled in VPS. The values ofvps_full_pic_width_in_luma_samples andvps_full_pic_height_in_luma_samples may be equal to the width and heightof the input picture(s), respectively.

In the same embodiment, the values of vps_full_pic_width_in_luma_samplesand vps_full_pic_height_in_luma_samples may not be used for decoding,but may be used for composition and display.

In the same embodiment, when the value of vps_sub_picture_dividing_flagis equal to 1, the syntax elements pic_offset_x and pic_offset_y may besignaled in SPS, which corresponds to (a) specific layer(s). In thiscase, the coded picture size (pic_width_in_luma_samples,pic_height_in_luma_samples) signaled in SPS may be equal to the widthand height of the sub-region corresponding to a specific layer. Also,the position (pic_offset_x, pic_offset_y) of the left-top corner of thesub-region may be signaled in SPS.

In the same embodiment, the position information (pic_offset_x,pic_offset_y) of the left-top corner of the sub-region may not be usedfor decoding, but may be used for composition and display.

In the same or another embodiment, the layout information (size andposition) of all or sub-set sub-region(s) of (an) input picture(s), thedependency information between layer(s) may be signaled in a parameterset or an SEI message. FIG. 18 shows an example of syntax elements toindicate the information o the layout of sub-regions, the dependencybetween layers, and the relation between a sub-region and one or morelayers. In this example, the syntax element num_sub_region indicates thenumber of (rectangular) sub-regions in the current coded video sequence.the syntax element num_layers indicates the number of layers in thecurrent coded video sequence. The value of num_layers may be equal to orgreater than the value of num_sub_region. When any sub-region is codedas a single layer, the value of num_layers may be equal to the value ofnum_sub_region. When one or more sub-regions are coded as multiplelayers, the value of num_layers may be greater than the value ofnum_sub_region. The syntax element direct_dependency_flag[i][j]indicates the dependency from the j-th layer to the i-th layer.num_layers_for_region[i] indicates the number of layers associated withthe i-th sub-region. sub_region_layer_id[i][j] indicates the layer_id ofthe j-th layer associated with the i-th sub-region. Thesub_region_offset_x[i] and sub_region_offset_y[i] indicate thehorizontal and vertical location of the left-top corner of the i-thsub-region, respectively. The sub_region_width [i] andsub_region_height[i] indicate the width and height of the i-thsub-region, respectively.

In one embodiment, one or more syntax elements that specify the outputlayer set to indicate one of more layers to be outputted with or withoutprofile tier level information may be signaled in a high-level syntaxstructure, e.g. VPS, DPS, SPS, PPS, APS or SEI message. Referring toFIG. 19 , the syntax element num_output_layer_sets indicating the numberof output layer set (OLS) in the coded vide sequence referring to theVPS may be signaled in the VPS. For each output layer set,output_layer_flag may be signaled as many as the number of outputlayers.

In the same embodiment, output_layer_flag[i] equal to 1 specifies thatthe i-th layer is output. vps_output_layer_flag[i] equal to 0 specifiesthat the i-th layer is not output.

In the same or another embodiment, one or more syntax elements thatspecify the profile tier level information for each output layer set maybe signaled in a high-level syntax structure, e.g. VPS, DPS, SPS, PPS,APS or SEI message. Still referring to FIG. 19 , the syntax elementnum_profile_tile_level indicating the number of profile tier levelinformation per OLS in the coded vide sequence referring to the VPS maybe signaled in the VPS. For each output layer set, a set of syntaxelements for profile tier level information or an index indicating aspecific profile tier level information among entries in the profiletier level information may be signaled as many as the number of outputlayers.

In the same embodiment, profile_tier_level_idx[i][j] specifies theindex, into the list of profile_tier_level( ) syntax structures in theVPS, of the profile_tier_level( ) syntax structure that applies to thej-th layer of the i-th OLS.

In the same or another embodiment, referring to FIG. 20 , the syntaxelements num_profile_tile_level and/or num_output_layer_sets may besignaled when the number of maximum layers is greater than 1(vps_max_layers_minus1>0).

In the same or another embodiment, referring to FIG. 20 , the syntaxelement vps_output_layers_mode[i] indicating the mode of output layersignaling for the i-th output layer set may be present in VPS.

In the same embodiment, vps_output_layers_mode[i] equal to 0 specifiesthat only the highest layer is output with the i-th output layer set.vps_output_layer_mode[i] equal to 1 specifies that all layers are outputwith the i-th output layer set. vps_output_layer_mode[i] equal to 2specifies that the layers that are output are the layers withvps_output_layer_flag[i][j] equal to 1 with the i-th output layer set.More values may be reserved.

In the same embodiment, the output_layer_flag[i][j] may or may not besignaled depending on the value of vps_output_layers_mode[i] for thei-th output layer set.

In the same or another embodiment, referring to FIG. 20 , the flagvps_ptl_signal_flag[i] may be present for the i-th output layer set.Depending the value of vps_ptl_signal_flag[i], the profile tier levelinformation for the i-th output layer set may or may not be signaled.

In the same or another embodiment, referring to FIG. 21 , the number ofsubpicture, max_subpics_minus1, in the current CVS may be signalled in ahigh-level syntax structure, e.g. VPS, DPS, SPS, PPS, APS or SEImessage.

In the same embodiment, referring to FIG. 21 , the subpictureidentifier, sub_pic_id[i], for the i-th subpicture may be signalled,when the number of subpictures is greater than 1 (max_subpics_minus1>0).

In the same or another embodiment, one or more syntax elementsindicating the subpicture identifier belonging to each layer of eachoutput layer set may be signalled in VPS. Referring to FIG. 22 , thesub_pic_id_layer[i][j][k], which indicates the k-th subpicture presentin the j-th layer of the i-th output layer set. With those information,a decoder may recognize which sub-picture may be decoded and outputtedfor each layer of a specific output layer set.

In an embodiment, picture header (PH) is a syntax structure containingsyntax elements that apply to all slices of a coded picture. A pictureunit (PU) is a set of NAL units that are associated with each otheraccording to a specified classification rule, are consecutive indecoding order, and contain exactly one coded picture. A PU may containa picture header (PH) and one or more VCL NAL units composing a codedpicture.

In an embodiment, an SPS (RBSP) may be available to the decoding processprior to it being referenced, included in at least one AU withTemporalId equal to 0 or provided through external means.

In an embodiment, an SPS (RBSP) may be available to the decoding processprior to it being referenced, included in at least one AU withTemporalId equal to 0 in the CVS, which contains one or more PPSreferring to the SPS, or provided through external means.

In an embodiment, an SPS (RBSP) may be available to the decoding processprior to it being referenced by one or more PPS, included in at leastone PU with nuh_layer_id equal to the lowest nuh_layer_id value of thePPS NAL units that refer to the SPS NAL unit in the CVS, which containsone or more PPS referring to the SPS, or provided through externalmeans.

In an embodiment, an SPS (RBSP) may be available to the decoding processprior to it being referenced by one or more PPS, included in at leastone PU with TemporalId equal to 0 and nuh_layer_id equal to the lowestnuh_layer_id value of the PPS NAL units that refer to the SPS NAL unitor provided through external means.

In an embodiment, an SPS (RBSP) may be available to the decoding processprior to it being referenced by one or more PPS, included in at leastone PU with TemporalId equal to 0 and nuh_layer_id equal to the lowestnuh_layer_id value of the PPS NAL units that refer to the SPS NAL unitin the CVS, which contains one or more PPS referring to the SPS, orprovided through external means or provided through external means.

In the same or another embodiment, pps_seq_parameter_set_id specifiesthe value of sps_seq_parameter_set_id for the referenced SPS. The valueof pps_seq_parameter_set_id may be the same in all PPSs that arereferred to by coded pictures in a CLVS.

In the same or another embodiment, all SPS NAL units with a particularvalue of sps_seq_parameter_set_id in a CVS may have the same content.

In the same or another embodiment, regardless of the nuh_layer_idvalues, SPS NAL units may share the same value space ofsps_seq_parameter_set_id.

In the same or another embodiment, the nuh_layer_id value of a SPS NALunit may be equal to the lowest nuh_layer_id value of the PPS NAL unitsthat refer to the SPS NAL unit.

In an embodiment, when an SPS with nuh_layer_id equal to m is referredto by one or more PPS with nuh_layer_id equal to n. the layer withnuh_layer_id equal to m may be the same as the layer with nuh_layer_idequal to n or a (direct or indirect) reference layer of the layer withnuh_layer_id equal to m.

In an embodiment, a PPS (RBSP) shall be available to the decodingprocess prior to it being referenced, included in at least one AU withTemporalId equal to the TemporalId of the PPS NAL unit or providedthrough external means.

In an embodiment, a PPS (RBSP) may be available to the decoding processprior to it being referenced, included in at least one AU withTemporalId equal to the TemporalId of the PPS NAL unit in the CVS, whichcontains one or more PHs (or coded slice NAL units) referring to thePPS, or provided through external means.

In an embodiment, a PPS (RBSP) may be available to the decoding processprior to it being referenced by one or more PHs (or coded slice NALunits), included in at least one PU with nuh_layer_id equal to thelowest nuh_layer_id value of the coded slice NAL units that refer to thePPS NAL unit in the CVS, which contains one or more PHs (or coded sliceNAL units) referring to the PPS, or provided through external means.

In an embodiment, a PPS (RBSP) may be available to the decoding processprior to it being referenced by one or more PHs (or coded slice NALunits), included in at least one PU with TemporalId equal to theTemporalId of the PPS NAL unit and nuh_layer_id equal to the lowestnuh_layer_id value of the coded slice NAL units that refer to the PPSNAL unit in the CVS, which contains one or more PHs (or coded slice NALunits) referring to the PPS, or provided through external means.

In the same or another embodiment, ph_pic_parameter_set_id in PHspecifies the value of pps_pic_parameter_set_id for the referenced PPSin use. The value of pps_seq_parameter_set_id may be the same in allPPSs that are referred to by coded pictures in a CLVS.

In the same or another embodiment, All PPS NAL units with a particularvalue of pps_pic_parameter_set_id within a PU shall have the samecontent.

In the same or another embodiment, regardless of the nuh_layer_idvalues, PPS NAL units may share the same value space ofpps_pic_parameter_set_id.

In the same or another embodiment, the nuh_layer_id value of a PPS NALunit may be equal to the lowest nuh_layer_id value of the coded sliceNAL units that refer to the NAL unit that refer to the PPS NAL unit.

In an embodiment, when a PPS with nuh_layer_id equal to m is referred toby one or more coded slice NAL units with nuh_layer_id equal to n. thelayer with nuh_layer_id equal to m may be the same as the layer withnuh_layer_id equal to n or a (direct or indirect) reference layer of thelayer with nuh_layer_id equal to m.

In an embodiment, a PPS (RBSP) shall be available to the decodingprocess prior to it being referenced, included in at least one AU withTemporalId equal to the TemporalId of the PPS NAL unit or providedthrough external means.

In an embodiment, a PPS (RBSP) may be available to the decoding processprior to it being referenced, included in at least one AU withTemporalId equal to the TemporalId of the PPS NAL unit in the CVS, whichcontains one or more PHs (or coded slice NAL units) referring to thePPS, or provided through external means.

In an embodiment, a PPS (RBSP) may be available to the decoding processprior to it being referenced by one or more PHs (or coded slice NALunits), included in at least one PU with nuh_layer_id equal to thelowest nuh_layer_id value of the coded slice NAL units that refer to thePPS NAL unit in the CVS, which contains one or more PHs (or coded sliceNAL units) referring to the PPS, or provided through external means.

In an embodiment, a PPS (RBSP) may be available to the decoding processprior to it being referenced by one or more PHs (or coded slice NALunits), included in at least one PU with TemporalId equal to theTemporalId of the PPS NAL unit and nuh_layer_id equal to the lowestnuh_layer_id value of the coded slice NAL units that refer to the PPSNAL unit in the CVS, which contains one or more PHs (or coded slice NALunits) referring to the PPS, or provided through external means.

In the same or another embodiment, ph_pic_parameter_set_id in PHspecifies the value of pps_pic_parameter_set_id for the referenced PPSin use. The value of pps_seq_parameter_set_id may be the same in allPPSs that are referred to by coded pictures in a CLVS.

In the same or another embodiment, All PPS NAL units with a particularvalue of pps_pic_parameter_set_id within a PU shall have the samecontent.

In the same or another embodiment, regardless of the nuh_layer_idvalues, PPS NAL units may share the same value space ofpps_pic_parameter_set_id.

In the same or another embodiment, the nuh_layer_id value of a PPS NALunit may be equal to the lowest nuh_layer_id value of the coded sliceNAL units that refer to the NAL unit that refer to the PPS NAL unit.

In an embodiment, when a PPS with nuh_layer_id equal to m is referred toby one or more coded slice NAL units with nuh_layer_id equal to n. thelayer with nuh_layer_id equal to m may be the same as the layer withnuh_layer_id equal to n or a (direct or indirect) reference layer of thelayer with nuh_layer_id equal to m.

In an embodiment, as shown in FIG. 22 , pps_subpic_id[i] in pictureparameter set specifies the subpicture ID of the i-th subpicture. Thelength of the pps_subpic_id[i] syntax element ispps_subpic_id_len_minus1+1 bits.

The variable SubpicIdVal[i], for each value of i in the range of 0 tosps_num_subpics_minus1, inclusive, is derived as follows:

for(i=0; i<=sps_num_subpics_minus1; i++)

if(subpic_id_mapping_explicitly_signalled_flag)

-   -   SubpicIdVal[i]=subpic_id_mapping_in_pps_flag? pps_subpic_id[i]:        sps_subpic_id[i]

else

-   -   SubpicIdVal[i]=i

In the same or another embodiment, for any two different values of i andj in the range of 0 to sps_num_subpics_minus1, inclusive, SubpicIdVal[i]may not be equal to SubpicIdVal[j].

In the same or another embodiment, when the current picture is not thefirst picture of the CLVS, for each value of i in the range of 0 tosps_num_subpics_minus1, inclusive, if the value of SubpicIdVal[i] is notequal to the value of SubpicIdVal[i] of the previous picture in decodingorder in the same layer, the nal_unit_type for all coded slice NAL unitsof the subpicture in the current picture with subpicture index i may beequal to a particular value in the range of IDR_W_RADL to CRA_NUT,inclusive.

In the same or another embodiment, when the current picture is not thefirst picture of the CLVS, for each value of i in the range of 0 tosps_num_subpics_minus1, inclusive, if the value of SubpicIdVal[i] is notequal to the value of SubpicIdVal[i] of the previous picture in decodingorder in the same layer, sps_independent_subpics_flag may be equal to 1.

In the same or another embodiment, when the current picture is not thefirst picture of the CLVS, for each value of i in the range of 0 tosps_num_subpics_minus1, inclusive, if the value of SubpicIdVal[i] is notequal to the value of SubpicIdVal[i] of the previous picture in decodingorder in the same layer, subpic_treated_as_pic_flag[i] andloop_filter_across_subpic_enabled_flag[i] may be equal to 1.

In the same or another embodiment, when the current picture is not thefirst picture of the CLVS, for each value of i in the range of 0 tosps_num_subpics_minus1, inclusive, if the value of SubpicIdVal[i] is notequal to the value of SubpicIdVal[i] of the previous picture in decodingorder in the same layer, sps_independent_subpics_flag shall be equal to1 or subpic_treated_as_pic_flag[i] andloop_filter_across_subpic_enabled_flag[i] shall be equal to 1.

In the same or another embodiment, when a subpicture is independentlyencoded without any reference to another subpicture, the value ofsubpicture identifier of a region may be changed within a coded videosequence.

The samples are processed in units of CTBs. The array size for each lumaCTB in both width and height is CtbSizeY in units of samples. The widthand height of the array for each chroma CTB are CtbWidthC andCtbHeightC, respectively, in units of samples. Each CTB is assigned apartition signalling to identify the block sizes for intra or interprediction and for transform coding. The partitioning is a recursivequadtree partitioning. The root of the quadtree is associated with theCTB. The quadtree is split until a leaf is reached, which is referred toas the quadtree leaf. When the component width is not an integer numberof the CTB size, the CTBs at the right component boundary areincomplete. When the component height is not an integer multiple of theCTB size, the CTBs at the bottom component boundary are incomplete.

The width and height information of each subpicture may be signaled inSPS in units of CtbSizeY. In FIG. 23 , for example,subpic_width_minus1[i] plus 1 specifies the width of the i-th subpicturein units of CtbSizeY. The length of the syntax element is Ceil(Log2((pic_width_max_in_luma_samples+CtbSizeY−1)>>CtbLog2SizeY))bits. Whennot present, the value of subpic_width_minus1[i] is inferred to be equalto((pic_width_max_in_luma_samples+CtbSizeY−1)>>CtbLog2SizeY)−subpic_ctu_top_left_x[i]−1. subpic_height_minus1[i] plus 1 specifies the height of thei-th subpicture in units of CtbSizeY. The length of the syntax elementis Ceil(Log2((pic_height_max_in_luma_samples+CtbSizeY−1)>>CtbLog2SizeY))bits. Whennot present, the value of subpic_height_minus1[i] is inferred to beequal to((pic_height_max_in_luma_samples+CtbSizeY−1)>>CtbLog2SizeY)−subpic_ctu_top_left_y[i]−1.

The width of each subpicture may be greater than or equal to CtbSizeY,when the picture width is greater than or equal to CtbSizeY. The heightof each subpicture may be greater than or equal to CtbSizeY, when thepicture height is greater than or equal to CtbSizeY.

If the picture width is not greater than CtbSizeY and the picture heightis not greater than CtbSizeY, the picture may not be partitioned intomore than one subpicture. In the case, the number of subpictures may beequal to 1.

When pic_width_max_in_luma_samples is not greater than CtbSizeY andpic_height_max_in_luma_samples is not greater than CtbSizeY, the valueof subpic_info_present_flag shall be equal to 0. Whensubpic_info_present_flag is equal to 0, no explicit signaling is presentfor subpicture partitioning information and the number of subpicture inthe picture is equal to 1.

In the same or another embodiment, sps_subpic_id_len_minus1 plus 1specifies the number of bits used to represent the syntax elementsps_subpic_id[i], the syntax elements pps_subpic_id[i], when present,and the syntax element slice_subpic_id, when present. The value ofsps_subpic_id_len_minus1 may be in the range of 0 to 15, inclusive. Thevalue of 1<<(sps_subpic_id_len_minus1) may be greater than or equal tosps_num_subpics_minus1+1.

In the same or another embodiment, when the number of subpictures isequal to 1, subpic_info_present_flag may be equal to 0 and thesubpicture partitioning information may not be explicitly signalled,because the subpicture width and height information is equal to thepicture width and height information and the left-top position of thesubpicture is equal to the left-top position of the picture in thatcase.

For example, subpic_ctu_top_left_x[i] specifies horizontal position oftop left CTU of i-th subpicture in unit of CtbSizeY. The length of thesyntax element is Ceil(Log2((pic_width_max_in_luma_samples+CtbSizeY−1)>>CtbLog2SizeY)) bits. Whennot present, the value of subpic_ctu_top_left_x[i] is inferred to beequal to 0. subpic_ctu_top_left_y[i] specifies vertical position of topleft CTU of i-th subpicture in unit of CtbSizeY. The length of thesyntax element is Ceil(Log2((pic_height_max_in_luma_samples+CtbSizeY−1)>>CtbLog2SizeY))bits. Whennot present, the value of subpic_ctu_top_left_y[i] is inferred to beequal to 0. subpic_width_minus1[i] plus 1 specifies the width of thei-th subpicture in units of CtbSizeY. The length of the syntax elementis Ceil(Log2((pic_width_max_in_luma_samples+CtbSizeY−1)>>CtbLog2SizeY))bits. Whennot present, the value of subpic_width_minus1[i] is inferred to be equalto((pic_width_max_in_luma_samples+CtbSizeY−1)>>CtbLog2SizeY)−subpic_ctu_top_left_x[i]−1. subpic_height_minus1[i] plus 1 specifies the height of thei-th subpicture in units of CtbSizeY. The length of the syntax elementis Ceil(Log2((pic_height_max_in_luma_samples+CtbSizeY−1)>>CtbLog2SizeY)) bits. Whennot present, the value of subpic_height_minus1[i] is inferred to beequal to((pic_height_max_in_luma_samples+CtbSizeY−1)>>CtbLog2SizeY)−subpic_ctu_top_left_y[i]−1.

In the same or another embodiment, when the number of subpictures isgreater than 1, subpic_info_present_flag may be equal to 1 and thesubpicture partitioning information may be explicitly signaled in aparameter set, as shown in FIG. 23 .

For example, in FIG. 23 , sps_num_subpics_minus2 plus 2 specifies thenumber of subpictures in each picture in the CLVS. The value ofsps_num_subpics_minus2 may be in the range of 0 toCeil(pic_width_max_in_luma_samples÷CtbSizeY)*Ceil(pic_height_max_in_luma_samples÷CtbSizeY)−2,inclusive. When not present, the value of sps_num_subpics_minus2 isinferred to be equal to 0.

In the same embodiment, the lists SubpicWidthInTiles[i] andSubpicHeightInTiles[i], for i ranging from 0 to sps_num_subpics_minus1,inclusive, specifying the width and the height of the i-th subpicture intile columns and rows, respectively, and the listsubpicHeightLessThanOneTileFlag[i], for i ranging from 0 tosps_num_subpics_minus1, inclusive, specifying whether the height of thei-th subpicture is less than one tile row, are derived as follows:

for(i=0; i<=sps_num_subpics_minus2+1; i++) {

leftX=subpic_ctu_top_left_x[i]

rightX=leftX+subpic_width_minus1[i]

SubpicWidthInTiles[i]=ctbToTileColIdx[rightX]+1−ctbToTileColIdx[leftX]

topY=subpic_ctu_top_left_y[i]

bottomY=topY+subpic_height_minus1[i]

SubpicHeightInTiles[i]=

ctbToTileRowIdx[bottomY]+1−ctbToTileRowIdx[topY]

if(SubpicHeightInTiles[i]==1 &&

-   -   subpic_height_minus1[i]+1<

RowHeight[ctbToTileRowIdx[topY]])

-   -   subpicHeightLessThanOneTileFlag[i]=1        else    -   subpicHeightLessThanOneTileFlag[i]=0        }

When rect_slice_flag is equal to 1, the list NumCtusInSlice[i] for iranging from 0 to num_slices_in_pic_minus1, inclusive, specifying thenumber of CTUs in the i-th slice, the list SliceTopLeftTileIdx[i] for iranging from 0 to num_slices_in_pic_minus1, inclusive, specifying thetile index of the tile containing the first CTU in the slice, and thematrix CtbAddrInSlice[i][j] for i ranging from 0 tonum_slices_in_pic_minus1, inclusive, and j ranging from 0 toNumCtusInSlice[i]−1, inclusive, specifying the picture raster scanaddress of the j-th CTB within the i-th slice, and the variableNumSlicesInTile[i], specifying the number of slices in the tilecontaining the i-th slice, are derived as follows:

if( single_slice_per_subpic_flag ) {  for( i = 0; i <=sps_num_subpics_minus2+1; i++ ) {   NumCtusInSlice[ i ] = 0   if(subpicHeightLessThanOneTileFlag[ i ] ) /* The slice consists of a numberof CTU rows in a tile. */    AddCtbsToSlice( i, subpic_ctu_top_left_x[ i],     subpic_ctu_top_left_x[ i ] + subpic_width_minus1[ i ] + 1,subpic_ctu_top_left_y[ i ],     subpic_ctu_top_left_y[ i ] +subpic_height_minus1[ i ] + 1 ) else { /* The slice consists of a numberof complete tiles covering a rectangular region. */    tileX =CtbToTileColBd[ subpic_ctu_top_left_x[ i ] ]    tile Y = CtbToTileRowBd[subpic_ctu_top_left_y[ i ] ]    for( j = 0; j < SubpicHeightInTiles[ i]; j++ )     for( k = 0; k < SubpicWidthInTiles[ i ]; k++ )     AddCtbsToSlice( i, tileColBd[ tileX + k ], tileColBd[ tileX + k + 1], tileRowBd[ tileY + j ],       tileRowBd[ tileY + j + 1 ] )   }  } }else {  tileIdx = 0  for( i = 0; i <= num_slices_in_pic_minus1; i++ )  NumCtusInSlice[ i ] = 0  for( i = 0; i <= num_slices_in_pic_minus1;i++ ) {   SliceTopLeftTileIdx[ i ] = tileIdx   tileX = tileIdx %NumTileColumns   tile Y = tileIdx / NumTileColumns   if( i <num_slices_in_pic_minus1 ) {    slice WidthInTiles[ i ] =slice_width_in_tiles_minus1[ i ] + 1    sliceHeightInTiles[ i ] =slice_height_in_tiles_minus1[ i ] + 1   } else {    sliceWidthInTiles[ i] = NumTileColumns − tileX    sliceHeightInTiles[ i ] = NumTileRows −tileY    Num SlicesInTile[ i ] = 1   }   if( slicWidthInTiles[ i ] ==1&& sliceHeightInTiles[ i ] = = 1 ) {    if( num_exp_slices_in_tile[ i ]= = 0 ) {     NumSlicesInTile[ i ] = 1     sliceHeightInCtus[ i ] =RowHeight[ SliceTopLeftTileIdx[ i ] / NumTileColumns ]    } else {    remainingHeightInCtbsY = RowHeight[ SliceTopLeftTileIdx[ i ] /NumTileColumns ]     for( j = 0; j < num_exp_slices_in_tile[ i ] − 1;j++ ) {      sliceHeightInCtus[ i + j ] =exp_slice_height_in_ctus_minus1[ i ][ j ] + 1     remainingHeightInCtbsY −= sliceHeightInCtus[ i + j ]     }    uniformSliceHeight = exp_slice_height_in_ctus_minus1[ i ][ j ] + 1    while( remainingHeightInCtbsY >= uniformSliceHeight ) {     sliceHeightInCtus[ i + j ] = uniformSliceHeight     remainingHeightInCtbsY −= uniformSliceHeight      j++     }     if(remainingHeightInCtbsY > 0 ) {      sliceHeightInCtus[ i + j ] =remainingHeightInCtbsY      j++     }     NumSlicesInTile[ i ] = j    }   ctbY = tileRowBd[ tileY ]    for( j = 0; j < NumSlicesInTile[ i ];j++ ) {     AddCtbsToSlice( i + j, tileColBd[ tileX ], tileColBd[tileX + 1 ],       ctbY, ctbY + sliceHeightInCtus[ i + j ] )     ctbY +=sliceHeightInCtus[ i + j ]    }    i += NumSlicesInTile[ i ] − 1   }else    for( j = 0; j < sliceHeightInTiles[ i ]; j++ )     for( k = 0; k< sliceWidthInTiles[ i ]; k++ )      AddCtbsToSlice( i, tileColBd[tileX + k ], tileColBd[ tileX + k + 1 ],       tileRowBd[ tileY + j ],tileRowBd[ tileY + j + 1 ] )   if( i < num_slices_in_pic_minus1 ) {   if( tile_idx_delta_present_flag )     tileIdx += tile_idx_delta[ i ]   else {     tileIdx += sliceWidthInTiles[ i ]     if( tileIdx % NumTileColumns = = 0 )      tileIdx += ( sliceHeightInTiles[ i ] − 1 ) *NumTileColumns    }   }  } }

Two or more independently coded subpictures may be merged into a codedpicture, so that the coded picture may be decoded and outputted as asingle picture.

When two or more independently coded subpictures are merged into a codedpicture, a coded picture may consist of VCL NAL units with two or moredifferent NAL unit types.

In FIG. 23 , sps_independent_subpics_flag equal to 1 specifies that allsubpicture boundaries in the CLVS are treated as picture boundaries andthere is no loop filtering across the subpicture boundaries.sps_independent_subpics_flag equal to 0 does not impose such aconstraint. When not present, the value of sps_independent_subpics_flagis inferred to be equal to 0.

In FIG. 23 , subpic_treated_as_pic_flag[i] equal to 1 specifies that thei-th subpicture of each coded picture in the CLVS is treated as apicture in the decoding process excluding in-loop filtering operations.subpic_treated_as_pic_flag[i] equal to 0 specifies that the i-thsubpicture of each coded picture in the CLVS is not treated as a picturein the decoding process excluding in-loop filtering operations. When notpresent, the value of subpic_treated_as_pic_flag[i] is inferred to beequal to sps_independent_subpics_flag. Whensubpic_treated_as_pic_flag[i] is equal to 1, it is a requirement ofbitstream conformance that all of the following conditions are true foreach output layer and its reference layers in an OLS that includes thelayer containing the i-th subpicture as an output layer:

-   -   All pictures in the output layer and its reference layers shall        have the same value of pic_width_in_luma_samples and the same        value of pic_height_in_luma_samples.    -   All the SPSs referred to by the output layer and its reference        layers shall have the same value of sps_num_subpics_minus1 and        shall have the same values of subpic_ctu_top_left_x[j],        subpic_ctu_top_left_y[j], subpic_width_minus1[j],        subpic_height_minus1[j], and        loop_filter_across_subpic_enabled_flag[j], respectively, for        each value of j in the range of 0 to sps_num_subpics_minus1,        inclusive.    -   All pictures in each access unit in the output layer and its        reference layers shall have the same value of SubpicIdVal[j] for        each value of j in the range of 0 to sps_num_subpics_minus1,        inclusive.

In FIG. 23 , loop_filter_across_subpic_enabled_flag[i] equal to 1specifies that in-loop filtering operations may be performed across theboundaries of the i-th subpicture in each coded picture in the CLVS.loop_filter_across_subpic_enabled_flag[i] equal to 0 specifies thatin-loop filtering operations are not performed across the boundaries ofthe i-th subpicture in each coded picture in the CLVS. When not present,the value of loop_filter_across_subpic_enabled_pic_flag[i] is inferredto be equal to 1−sps_independent_subpics_flag.

The virtual boundary information may be signaled in a parameter set(e.g. SPS, PPS) or in a picture header or slice header. When a virtualboundary is present, any in-loop filtering process may be disallowedacross the virtual boundary.

In an embodiment, In FIG. 24 , the virtual boundary information issignalled in SPS. sps_virtual_boundaries_enabled_flag equal to 1specifies that disabling in-loop filtering across virtual boundaries maybe applied in the coded pictures in the CLVS.sps_virtual_boundaries_enabled_flag equal to 0 specifies that disablingin-loop filtering across virtual boundaries is not applied in the codedpictures in the CLVS. In-loop filtering operations include thedeblocking filter, sample adaptive offset filter, and adaptive loopfilter operations.

sps_virtual_boundaries_present_flag equal to 1 specifies thatinformation of virtual boundaries is signalled in the SPS.sps_virtual_boundaries_present_flag equal to 0 specifies thatinformation of virtual boundaries is not signalled in the SPS. Whenthere is one or more than one virtual boundaries signalled in the SPS,the in-loop filtering operations are disabled across the virtualboundaries in pictures referring to the SPS. In-loop filteringoperations include the deblocking filter, sample adaptive offset filter,and adaptive loop filter operations. It is a requirement of bitstreamconformance that when the value of res_change_in_clvs_allowed_flag isequal to 1, the value of sps_virtual_boundaries_present_flag shall beequal to 0. sps_num_ver_virtual_boundaries specifies the number ofsps_virtual_boundaries_pos_x[i] syntax elements that are present in theSPS. When sps_num_ver_virtual_boundaries is not present, it is inferredto be equal to 0. sps_virtual_boundaries_pos_x[i] specifies the locationof the i-th vertical virtual boundary in units of luma samples dividedby 8. The value of sps_virtual_boundaries_pos_x[i] shall be in the rangeof 1 to Ceil(pic_width_max_in_luma_samples÷8)−1, inclusive.sps_num_hor_virtual_boundaries specifies the number ofsps_virtual_boundaries_pos_y[i] syntax elements that are present in theSPS. When sps_num_hor_virtual_boundaries is not present, it is inferredto be equal to 0.

When sps_virtual_boundaries_enabled_flag is equal to 1 andsps_virtual_boundaries_present_flag is equal to 1, the sum ofsps_num_ver_virtual_boundaries and sps_num_hor_virtual_boundaries shallbe greater than 0.

sps_virtual_boundaries_pos_y[i] specifies the location of the i-thhorizontal virtual boundary in units of luma samples divided by 8. Thevalue of sps_virtual_boundaries_pos_y[i] shall be in the range of 1 toCeil(pic_height_max_in_luma_samples÷8)−1, inclusive.

In an embodiment, in FIG. 25 , ph_virtual_boundaries_present_flag equalto 1 specifies that information of virtual boundaries is signalled inthe PH. ph_virtual_boundaries_present_flag equal to 0 specifies thatinformation of virtual boundaries is not signalled in the PH. When thereis one or more than one virtual boundaries signalled in the PH, thein-loop filtering operations are disabled across the virtual boundariesin the picture. The in-loop filtering operations include the deblockingfilter, sample adaptive offset filter, and adaptive loop filteroperations. When not present, the value ofph_virtual_boundaries_present_flag is inferred to be equal to 0. It is arequirement of bitstream conformance that, when subpic_info_present_flagis equal to 1, the value of ph_virtual_boundaries_present_flag shall beequal to 0.

The variable VirtualBoundariesPresentFlag is derived as follows:

VirtualBoundariesPresentFlag=0

if(sps_virtual_boundaries_enabled_flag)

VirtualBoundariesPresentFlag=sps_virtual_boundaries_present_flag∥

-   -   ph_virtual_boundaries_present_flag

ph_num_ver_virtual_boundaries specifies the number ofph_virtual_boundaries_pos_x[i] syntax elements that are present in thePH. When ph_num_ver_virtual_boundaries is not present, it is inferred tobe equal to 0.

The variable NumVerVirtualBoundaries is derived as follows:

NumVerVirtualBoundaries=0

if(sps_virtual_boundaries_enabled_flag)

NumVerVirtualBoundaries=sps_virtual_boundaries_present_flag?

-   -   sps_num_ver_virtual_boundaries:ph_num_ver_virtual_boundaries

ph_virtual_boundaries_pos_x[i] specifies the location of the i-thvertical virtual boundary in units of luma samples divided by 8. Thevalue of ph_virtual_boundaries_pos_x[i] shall be in the range of 1 toCeil(pic_width_in_luma_samples÷8)−1, inclusive.

The list VirtualBoundariesPosX[i] for i ranging from 0 toNumVerVirtualBoundaries−1, inclusive, in units of luma samples,specifying the locations of the vertical virtual boundaries, is derivedas follows:

for(i=0; i<NumVerVirtualBoundaries; i++)

VirtualBoundariesPosX[i]=(sps_virtual_boundaries_present_flag?

-   -   sps_virtual_boundaries_pos_x[i]:ph_virtual_boundaries_pos_x[i])*8

The distance between any two vertical virtual boundaries shall begreater than or equal to CtbSizeY luma samples.

ph_num_hor_virtual_boundaries specifies the number ofph_virtual_boundaries_pos_y[i] syntax elements that are present in thePH. When ph_num_hor_virtual_boundaries is not present, it is inferred tobe equal to 0.

The parameter NumHorVirtualBoundaries is derived as follows:

NumHorVirtualBoundaries=0

if(sps_virtual_boundaries_enabled_flag)

NumHorVirtualBoundaries=sps_virtual_boundaries_present_flag?

-   -   sps_num_hor_virtual_boundaries:ph_num_hor_virtual_boundaries

When sps_virtual_boundaries_enabled_flag is equal to 1 andph_virtual_boundaries_present_flag is equal to 1, the sum ofph_num_ver_virtual_boundaries and ph_num_hor_virtual_boundaries shall begreater than 0.

When a picture may be composed of VCL NAL units with different NAL unittypes, the virtual boundary information may be signaled in SPS. In thatcase, the virtual boundary information may not be signaled in pictureheader.

When two or more coded subpictures are merged into a coded picture, thevirtual boundary information may be rewritten. If the virtual boundaryinformation is signaled in picture header or slice header, it makes themerge process complicated.

In an embodiment, when mixed_nalu_types_in_pic_flag is equal to 1, thevalue of ph_virtual_boundaries_present_flag shall be equal to 0.

In an embodiment, the virtual boundary information is signaled in PPS,when the virtual boundary information is not signaled in SPS.

In the same embodiment, for example in FIG. 26 ,pps_virtual_boundaries_present_flag equal to 1 specifies thatinformation of virtual boundaries is signalled in the PPS.pps_virtual_boundaries_present_flag equal to 0 specifies thatinformation of virtual boundaries is not signalled in the PPS. Whenthere is one or more than one virtual boundaries signalled in the PPS,the in-loop filtering operations are disabled across the virtualboundaries in the picture. The in-loop filtering operations include thedeblocking filter, sample adaptive offset filter, and adaptive loopfilter operations. When not present, the value ofpps_virtual_boundaries_present_flag is inferred to be equal to 0.

When sps_virtual_boundaries_present_flag is equal to 1,pps_virtual_boundaries_present_flag shall be equal to 0.

It is a requirement of bitstream conformance that, whensubpic_info_present_flag is equal to 1, the value ofpps_virtual_boundaries_present_flag shall be equal to 0.

The variable VirtualBoundariesPresentFlag is derived as follows:

VirtualBoundariesPresentFlag=0

if(sps_virtual_boundaries_enabled_flag)

VirtualBoundariesPresentFlag=sps_virtual_boundaries_present_flag∥

-   -   pps_virtual_boundaries_present_flag

pps_num_ver_virtual_boundaries specifies the number ofpps_virtual_boundaries_pos_x[i] syntax elements that are present in thePH. When pps_num_ver_virtual_boundaries is not present, it is inferredto be equal to 0.

The variable NumVerVirtualBoundaries is derived as follows:

NumVerVirtualBoundaries=0

if(sps_virtual_boundaries_enabled_flag)

NumVerVirtualBoundaries=sps_virtual_boundaries_present_flag?

-   -   sps_num_ver_virtual_boundaries:pps_num_ver_virtual_boundaries

pps_virtual_boundaries_pos_x[i] specifies the location of the i-thvertical virtual boundary in units of luma samples divided by 8. Thevalue of pps_virtual_boundaries_pos_x[i] shall be in the range of 1 toCeil(pic_width_in_luma_samples÷8)−1, inclusive.

The list VirtualBoundariesPosX[i] for i ranging from 0 toNumVerVirtualBoundaries−1, inclusive, in units of luma samples,specifying the locations of the vertical virtual boundaries, is derivedas follows:

for(i=0; i<NumVerVirtualBoundaries; i++)

VirtualBoundariesPosX[i]=(sps_virtual_boundaries_present_flag?

-   -   sps_virtual_boundaries_pos_x[i]:pps_virtual_boundaries_pos_x[i])*8

The distance between any two vertical virtual boundaries shall begreater than or equal to CtbSizeY luma sample.

While this disclosure has described several exemplary embodiments, thereare alterations, permutations, and various substitute equivalents, whichfall within the scope of the disclosure. It will thus be appreciatedthat those skilled in the art will be able to devise numerous systemsand methods which, although not explicitly shown or described herein,embody the principles of the disclosure and are thus within the spiritand scope thereof.

What is claimed is:
 1. A method, executable by a processor, the methodcomprising: receiving video data comprising a base layer, and one ormore enhancement layers that correspond to one or more subpictures, theone or more subpictures having one or more virtual boundaries;signaling, in a sequence parameter set, a syntax elementsps_virtual_boundaries_enabled_flag specifying whether virtualboundaries are enabled for the video data; when the syntax elementsps_virtual_boundaries_enabled_flag equals 1, specifying that virtualboundaries are enabled, signaling, in a picture parameter set or apicture header, a second syntax elementpps_virtual_boundaries_present_flag specifying whether information ofthe one or more virtual boundaries is signaled in the picture parameterset, and a third syntax element ph_virtual_boundaries_present_flagspecifying whether information of the one or more virtual boundaries issignaled in the picture header; when the information specifies that theinformation of the one or more virtual boundaries is signaled in thepicture parameter set or the picture header, signaling, in the pictureparameter set or the picture header associated with the received videodata, information corresponding to a number of the one or more virtualboundaries; and decoding the video data based on the signaledinformation corresponding to the virtual boundaries.
 2. The method ofclaim 1, wherein based on a virtual boundary being detected, in-loopfiltering is disabled across the virtual boundary.
 3. The method ofclaim 2, wherein the in-loop filtering comprises one or more from amonga deblocking filter, a sample adaptive offset filter, and an adaptiveloop filter.
 4. The method of claim 1, further comprising: reorganizingthe one or more subpictures; and updating the information specifyingwhether the one or more virtual boundaries are present at a picturelevel.
 5. The method of claim 1, wherein a distance between two verticalboundaries is specified to be greater than or equal to a sizecorresponding to a luma sample associated with the received video data.6. The method of claim 1, wherein the information specifying whether theone or more virtual boundaries are present is signaled in the pictureparameter set when not signaled in the sequence parameter set.
 7. Themethod of claim 1, wherein the sequence parameter set includes a signalof the number of vertical virtual boundaries and the number ofhorizontal virtual boundaries.
 8. The method of claim 1, wherein thepicture parameter set includes a signal of the number of verticalvirtual boundaries and the number of horizontal virtual boundaries. 9.The method of claim 1, wherein the picture header includes a signal ofthe number of vertical virtual boundaries and the number of horizontalvirtual boundaries.
 10. A computer system for coding video data, thecomputer system comprising: one or more computer-readable non-transitorystorage media configured to store computer program code; and one or morecomputer processors configured to access said computer program code andoperate as instructed by said computer program code, said computerprogram code including: receiving code configured to cause the one ormore computer processors to receive video data comprising a base layer,and one or more enhancement layers that correspond to one or moresubpictures, the one or more subpictures having one or more virtualboundaries; first signaling code configured to cause the one or morecomputer processors to signal, in a sequence parameter set, a syntaxelement sps_virtual_boundaries_enabled_flag specifying whether virtualboundaries are enabled for the video data; second signaling codeconfigured to cause the one or more computer processors to, when thesyntax element sps_virtual_boundaries_enabled_flag equals 1, specifyingthat virtual boundaries are enabled, signal, in, a picture parameter setor a picture header, a second syntax elementpps_virtual_boundaries_present_flag specifying whether information ofthe one or more virtual boundaries is signaled in, the picture parameterset, and a third syntax element ph_virtual_boundaries_present_flagspecifying whether information of the one or more virtual boundaries issignaled on the picture header; third signaling code configured to causethe one or more computer processors to, when the information specifiesthat the information of the one or more virtual boundaries is signaledin, the picture parameter set or the picture header, signal, in, thepicture parameter set or the picture header associated with the receivedvideo data, information corresponding to a number of the one or morevirtual boundaries; and decoding code configured to cause the one ormore computer processors to decode the video data based on the signaledinformation corresponding to the virtual boundaries.
 11. The computersystem of claim 10, wherein based on a virtual boundary being detected,in-loop filtering is disabled across the virtual boundary.
 12. Thecomputer system of claim 11, wherein the in-loop filtering comprises oneor more from among a deblocking filter, a sample adaptive offset filter,and an adaptive loop filter.
 13. The computer system of claim 10,further comprising: reorganizing code configured to cause the one ormore computer processors to reorganize the one or more subpictures andupdating code configured to cause the one or more computer processors toupdate the information specifying whether the one or more virtualboundaires are present at a picture level.
 14. The computer system ofclaim 10, wherein a distance between two vertical boundaries isspecified to be greater than or equal to a size corresponding to a lumasample associated with the received video data.
 15. The computer systemof claim 10, wherein the information specifying whether the one or morevirtual boundaries are present is signaled in the picture parameter setwhen not signaled in the sequence parameter set.
 16. A non-transitorycomputer readable medium having stored thereon a computer program forcoding video data, the computer program configured to cause one or morecomputer processors to: receive video data comprising a base layer, andone or more enhancement layers that correspond to one or moresubpictures, the one or more subpictures having one or more virtualboundaries; signaling, in a sequence parameter set, a syntax elementsps_virtual_boundaries_enabled_flag specifying whether virtualboundaries are enabled for the video data; when the syntax elementsps_virtual_boundaries_enabled_flag equals 1, specifying that virtualboundaries are enabled, signaling, in, a picture parameter set or apicture header, a second syntax elementpps_virtual_boundaries_present_flag specifying whether information ofthe one or more virtual boundaries is signaled in, the pictureparameters set, and a third syntax elementph_virtual_boundaries_present_flag specifying whether information of theone or more virtual boundaries is signaled in the picture header; whenthe information specifies that the information of the one or morevirtual boundaries is signaled in, the picture parameter set or thepicture header, signaling, in, the picture parameter set or the pictureheader associated with the received video data, informationcorresponding to a number of the one or more virtual boundaries; anddecode the video data based on the signaled information corresponding tothe virtual boundaries.
 17. The computer readable medium of claim 16,wherein based on a virtual boundary being detected, in-loop filtering isdisabled across the virtual boundary.
 18. The computer readable mediumof claim 17, wherein the in-loop filtering comprises one or more fromamong a deblocking filter, a sample adaptive offset filter, and anadaptive loop filter.
 19. The computer readable medium of claim 16,further comprising: reorganizing code configured to cause the one ormore computer processors to reorganize the one or more subpictures andupdating code configured to cause the one or more computer processors toupdate the information specifying whether the one or more virtualboundaries are present at a picture level.
 20. The computer readablemedium of claim 16, wherein a distance between two vertical boundariesis specified to be greater than or equal to a size corresponding to aluma sample associated with the received video data.